12 September 2013

Presence of Atmosphere and Water on Saturn Moon Titan Provides Deeper Understanding on Evolution of Life on Earth

At a symposium presented by the American Chemical Society, "Chemical Frontiers in Solar System Exploration", scientists have gathered to discuss the possibility and the circumstances that could lead to the evolution of life in one of the moons of Saturn, Titan.

Titan is one of the 62 satellites orbiting the planet Saturn. Located around one billion miles away from Earth, it is the only satellite in the solar system that is observed to have an atmosphere. The atmosphere consists of nitrogen and methane and also includes organic compounds such as ethane, acetylene, hydrogen cyanide, and cyanoacetylene.

The circumstances around Titan and its atmosphere closely resembles that of the Earth more than 3.5 billion years ago.

Data about Titan was gathered using the Huygens probe that landed on its surface on January 2005. For 90 minutes after touchdown, the probe transmitted its findings as well as images back to the Earth. The Huygens probe is the farthest landing for any craft launched from the Earth.

Based on the findings, Titan is the only object in the solar system apart from the Earth that contains large amounts of organic substances on the surface.

The symposium also covers the latest discoveries in space science, and experimental design and devices that are pushing the field to new levels. Other topics covering more than 30 presentations in the symposium are:

  • Molecules and molecular evolution in cold extraterrestrial environments: The chemist's approach
  • Ice-gas interactions during planet formation
  • Composition and chemical history of early solar system ices
  • OSIRIS-REx will return a sample of asteroid 1999 RQ36 for astrochemistry
  • Chemistry of star and planet formation
  • Low-temperature chemical reactions
  • New analytical techniques to study molecular interactions in space.

The abstracts of these presentations are enumerated below.

Titan and Evolution of Life

Glimpses of the events that nurtured life on Earth more than 3.5 billion years ago are coming from an unlikely venue almost 1 billion miles away, according to the leader of an effort to understand Titan, one of the most unusual moons in the solar system.

In a talk here today at the 246th National Meeting & Exposition of the American Chemical Society (ACS), the world's largest scientific society, Jonathan Lunine, Ph.D., said that Titan, the largest of Saturn's several dozen moons, is providing insights into the evolution of life unavailable elsewhere. The meeting, which features almost 7,000 presentations on new discoveries in science and other topics, continues through Thursday in the Indiana Convention Center and downtown hotels.

"Data sent back to Earth from space missions allow us to test an idea that underpins modern science's portrait of the origin of life on Earth," Lunine said. "We think that simple organic chemicals present on the primordial Earth, influenced by sunlight and other sources of energy, underwent reactions that produced more and more complex chemicals. At some point, they crossed a threshold — developing the ability to reproduce themselves. Could we test this theory in the lab? These processes have been underway on Titan for billions of years. We don't have a billion years in the lab. We don't even have a thousand years."

Lunine, who is with Cornell University and is one of about 260 scientists involved with the Cassini-Huygens mission, explained that only two celestial objects in the solar system have the large amounts of organic substances on their surfaces to provide such information. They are Titan and Earth. Organic substances on Earth, however, have been cycled through living things countless times. Titan's organic materials, which include deposits of methane and other hydrocarbons as large as some of the Great Lakes, are in pristine condition — never, so far as anyone knows, in contact with life.

Video: Titan - A Place Like Home (BBC Documentary)

Titan is the only moon in the solar system known to have an atmosphere. Like Earth, most of it consists of nitrogen, with methane the second-most abundant. Sunlight strikes Titan's upper atmosphere, breaking that compound into pieces that react with each other and nitrogen to form organic compounds. Those include ethane, acetylene, hydrogen cyanide, cyanoacetylene and others — all familiar terrestrial chemicals.

"We've got a very good inventory of what's there in the atmosphere," Lunine said. "What we've only recently begun to understand is the fate of these organics at the surface of Titan."

Lunine explained that for a long time, Mars had captured the public's and scientists' imagination as a possible location to find interesting organic chemistry and hints at life outside the Earth — and for good reason: It is an Earth-like planet relatively close to the Sun. But scientists have only found simple organic materials on the red planet.

Recent research has provided fascinating hints that liquid water may exist deep under Titan's surface. Other data suggest that areas of Titan's seafloor may be similar to areas of Earth's seafloors where hydrothermal vents exist. These passways into Earth's interior spout hot, mineral-rich water that fosters an array of once-unknown forms of life. Lunine also cited research that has identified prime potential landing spots on Titan should the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) or other space agencies decide on another mission to Titan.

Scientists now know, thanks to the joint NASA-ESA spacecraft that arrived at Saturn in 2004 after a seven-year journey through the solar system, that Titan shares a surprising number of features with Earth. The enormous volumes of data that Cassini's 12 scientific instruments and the Huygens surface probe streamed back to Earth paint a complex picture of Titan's surface and the dense atmosphere that enshrouds it. Rivers flow into lakes. Wind sweeps across dunes. Giant storms brew, and clouds float across the hazy sky.

The catch is that Titan, nearly a billion miles from the Sun and a little larger than the Earth's own moon, is mostly frozen. It only receives about 1 percent of the sunlight that Earth gets. As a result, it is unimaginably frigid. At minus 290 degrees Fahrenheit — that's 160 degrees colder than the coldest recorded temperature in Antarctica — its water ice is rock solid, at least on the surface. And the rivers and lakes? They are made of liquid hydrocarbons, ethane and methane, which on balmy Earth are the main components of natural gas. Titan's deposits may be 10-100 times greater than all of Earth's oil and gas reserves, estimates suggest.

Size comparison of Saturn moon Titan, the Moon, and Earth

Lunine acknowledged funding from the Cassini Project, the NASA Astrobiology Institute and the John Templeton Foundation.

Abstracts of Presentations at Chemical Frontiers in Solar System Exploration

Titan's surface chemical evolution

Jonathan I Lunine
Department of Astronomy
Cornell University
Ithaca, NY 14853, United States

Titan, Saturn's largest moon, has a surface whose underlying bedrock is water ice but for which the overlying sediments are organic molecules. Under the dense nitrogen-methane atmosphere, from which a variety of nitriles and hydrocarbons precipitate, the surface organics are organized into dune fields, and at high latitudes, liquid hydrocarbon lakes and seas. Cassini and Huygens observations indicate that surface chemical evolution takes place, for example conversion of acetylene to benzene and (possibly) with hydrogen cyanide to acetonitrile and cyanoacetylene. Observations of the area around the lakes and seas suggest that "evaporite" deposits of refractory hydrocarbons and nitriles are present. The chemical evolution of this material, under study by computer simulations at present, makes such sites of primary interest for future landed missions.

Molecules and molecular evolution in cold extraterrestrial environments: The chemist's approach

Reggie L. Hudson, Perry A. Gerakines, Mark J. Loeffler, Marla H. Moore, Robert F. Ferrante.
Astrochemistry Laboratory
NASA Goddard Space Flight Center
Greenbelt, Maryland 20771, United States

Department of Chemistry
US Naval Academy
Annapolis, Maryland 21402, United States

Astrochemical research has been conducted at NASA's Cosmic Ice Laboratory for over 30 years with an emphasis on the thermal, photo-, and radiation chemistries and IR spectroscopy of small molecules in the solid phase. Applications include the measurements of spectral properties, syntheses of some presumed-unstable molecules, and the prediction and identification of new extraterrestrial species. This presentation for the inaugural meeting of the ACS Astrochemistry Subdivision will cover some of our lab's past work, highlight some difficulties, and present some newer results, particularly as relevant to Solar System chemistry. We acknowledge the support of NASA's Cassini Data Analysis, Planetary Geology and Geophysics, Outer Planets Research, Mars Fundamental Research, Planetary Atmospheres, and Exobiology programs, as well as the NASA Astrobiology Institute's Goddard Center for Astrobiology.

Ice-gas interactions during planet formation

Karin I Öberg, Chunhua Qi, David Wilner, Edwin Bergin.
Department of Chemistry
University of Virginia
Charlottesville, VA 22904, United States

Harvard-Smithsonian Center for Astrophysics
Cambridge, MA 02138, United States

Department of Astronomy
University of Michigan
Ann Arbor, MI 48109, United States

Planets form in disks around young stars. The main component of such disks, cold H2, cannot be observed directly and we therefore rely on observations of minor constituents, dust and trace molecules, to characterize disk structures and compositions. Molecular abundances are generally sensitive to their local environment and spatially and spectrally resolved observations of molecular lines have a large untapped potential as probes of disk density, temperature and radiation profiles. Molecular abundances are also important to characterize in their own right, to constrain the bulk composition of forming planets, and the presence of complex organic species. Interpretations of molecular line observations depend critically on our understanding of molecular formation and destruction mechanisms, however, which is often limited, especially for chemical processes in the icy mantles of dust grains.

I will present new millimeter wavelength molecular line observations from the Atacama Large Millimeter Array (ALMA) and the Submillimeter Array (SMA) toward a sample of protoplanetary disks and discuss how these chemical images, together with complementary observations and laboratory astrochemical experiments, constrain the chemical pathways active during planet formation. I will focus on interactions between gas-phase molecules and icy grain mantles and ice chemistry, since interstellar ices are crucial both for the development of molecular complexity during star and planet formation, and for planet formation efficiencies. Based on the analysis, I will present new constraints on condensation lines in protoplanetary disks, and their potential effects on planet formation and complex molecule formation in the outer solar system.

Images from the Cassini mission show river networks draining into lakes in Titan's north polar region.

Composition and chemical history of early solar system ices

Adwin Boogert
Infrared Processing and Analysis Center (IPAC)
California Insitute of Technology
Pasadena, CA 91125, United States

Some models of protostellar collapse [1] indicate that all but the most volatile ices from the native envelope survive the infall phase, at least at larger disk radii (10 AU). The composition and chemical history of ices in circumstellar envelopes, and sometimes in disks, can be traced with infrared (2-30 micron) spectroscopy using ground and space based telescopes. Surveys of large samples of Young Stellar Objects (YSOs) [2,3,4] and quiescent clouds [5,6] have shown that the ice abundances and band profiles vary considerably as a function of environment. A rather complex mixture of simple species (CH3OH, CO2, H2O, NH3, CO) exists even before stars form, most likely reflecting a history of chemistry on cold grain surfaces. CH3OH abundance variations show that local physical conditions (CO freeze out) and time scales (CH3OH formation) are key factors in this early chemistry. Sublimation and thermal processing of the ices are dominant processes during the YSO's evolution. But, contrary to present day solar system ices, the evidence of processing of interstellar and circumstellar ices by photons and energetic particles is weak. Laboratory experiments are needed to further constrain the processes of molecule formation as well as to determine the origin of several unidentified ice features. Such experiments will also be essential to interpret the sensitive and high spectral resolution observations that will become possible with new facilities (the SOFIA airplane and JWST satellite).

OSIRIS-REx will return a sample of asteroid 1999 RQ36 for astrochemistry

Jason P Dworkin, OSIRIS-REx Team.
Astrochemistry Laboratory
Code 691.0
NASA Goddard Space Flight Center, Greenbelt
MD 20771, United States,

United States

Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) is the third mission in NASA's New Frontiers program. OSIRIS-REx launches in 2016 and will return the first pristine samples of carbonaceous material from the surface of a primitive asteroid in 2023. The target, (101955) 1999 RQ36, is 1/2 km diameter roughly spherical Apollo near-Earth asteroid. It is expected to be carbonaceous, similar to CI or CM carbonaceous chondrites. This organic-rich remnant from the early Solar System is also among the most potentially hazardous asteroids known with a 1 in 2500 chance of impacting the Earth in the late 22nd century. OSIRIS-REx will measure the Yarkovsky effect to better constrain future orbit and impact potential of this and other asteroids. OSIRIS-REx will image, map, and spectrally characterize RQ36 from 0.4-50µm. The returned sample of regolith will be >60g (and up to 2kg) and thus the largest extraterrestrial sample returned from space since Apollo 17. Unlike meteorites, the sample will come from a known, well-characterized source and will be collected and transported to Earth pristine from terrestrial contamination. It will be available for study by the global astrochemistry community to address fundamental questions about the origin and evolution of the solar system and the life it harbors.

Still image of Titan's surface captured by the Huygens probe

Laboratory measurements of chemical reactions for atmospheres of the Outer Planets and Titan

Regina J Cody, Ramsey L. Smith.
Astrochemistry Laboratory
NASA Goddard Space Flight Center
Greenbelt, MD 20771, United States

Planetary Systems Laboratory
NASA Goddard Space Flight Center
Greenbelt, MD 20771, United States

Understanding the complex chemistry of the planetary and satellite atmospheres requires the close collaboration of compositional observations, photochemical models, and laboratory kinetic measurements of critical chemical reactions. The laboratory measurements need to be made under physical conditions as close as possible to that present in the atmospheres. This is challenging for measurements of reactions intended for the atmospheres of the Outer Planets and Titan because both low pressures and low temperatures are needed. Additionally, many of the reactions are fast due to radical or atom reactants. We use an experimental technique developed specifically for these types of kinetic measurements. A microwave discharge fast flow tube (2000 cm/sec) is coupled with a quadrupole mass spectrometer for detection of a broad range of reactants or products. Fluorine atoms generated in the microwave discharge are reacted with a stable parent molecule to generate the radicals, generally at low concentrations so that the measurements follow first order kinetics. The second reactant is added through a movable probe, and distance is converted to time. In the mass spectrometer low energy electron impact ionization greatly reduces, if not eliminates, interferences in the detection of the species for which kinetics is being measured. The kinetic measurements can be made in the pressure range of 0.5-2 Torr and 150-300K. The lower ends of these ranges tend to correspond to the physical conditions of the planetary or satellite stratospheres. Currently we are undertaking measurements of isotopic methane.

Molecular beam and theoretical studies on the reaction dynamics of N(2D) and CN radicals relevant to the atmospheric chemistry of Titan

Nadia Balucani, Francesca Leonori, Dimitrios Skouteris, Marzio Rosi, Piergiorgio Casavecchia.
Department of Chemistry
Università degli Studi di Perugia
Perugia, PG 06125, Italy

The atmosphere of Titan is mainly composed of molecular nitrogen, with a few percent of methane and small amounts of hydrocarbons as well as traces of nitrogen and oxygen-bearing species. Nitrogen atoms in the excited metastable2D state can be produced in the upper atmosphere by several processes involving N2 (photodissociation, electron dissociation, etc.). Since deactivation of N(2D) by N2 is a slow process, the main fate of N(2D) above 800 km is chemical reaction with other constituents of Titan's atmosphere. In order to assess the role of N(2D) reactions and improve our understanding of the neutral chemistry that controls the formation of N-containing organic compounds in the atmosphere of Titan, as well as that of other bodies where both N2 and hydrocarbons are present, such as Uranus and Neptune, there is the need of measuring reaction rate constants at the relevant temperatures -- and this can be best done using the CRESU kinetics technique -- but also to know the primary reaction products as well as their branching ratios (BRs), because this can strongly affect the accuracy of photochemical models. Primary products and BRs can be best obtained from crossed molecular beam (CMB) experiments with mass-spectrometric detection, empowered with soft ionization detection. Interpretation of CMB results is often assisted by ab initio calculations of the underlying potential energy surfaces and RRKM statistical estimates, and possibly also dynamics computations, of BRs. In this talk we will focus on our recent CMB and theoretical studies of reactions relevant to the atmosphere of Titan, such as those of N(2D) with methane, ethane, acetylene, ethylene, hydrogen and water. Results on reactions of CN radicals with unsaturated hydrocarbons will also be discussed briefly. Acknowledgements. This research is supported by MIUR (PRIN 2010-2011) and EC COST action CM0805 "The Chemical Cosmos".

Low temperature reaction kinetics and organic synthesis in space: Organonitrogen chemistry

Ian R Sims, Sidaty Cheikh Sid Ely, Martin Fournier, Jean-Claude Guillemin, Stephen J Klippenstein.
Department of Molecular Physics
University of Rennes 1
Institute of Physics, Rennes, France

Department of Organic and Supramolecular Chemistry
Ecole Nationale Superieure de Chimie de Rennes
Rennes, France

Chemical Sciences and Engineering Division
Argonne National Laboratory
Argonne, Illinois IL60439, United States

Orange haze of Titan
I will give an overview of the importance of determining temperature dependant rate constants for elementary chemical reactions for understanding the creation and destruction of organic matter in space. In particular I will focus on studies of the reactivity of carbon-containing radical species with organic co-reagents leading to efficient molecular growth even at the low temperatures of dense interstellar clouds (10-20 K) or of the atmospheres of planets and their moons, such as that of Titan (70-180 K), studied using both pulsed1 and continuous flow CRESU2 (Cinétique de Réaction en Ecoulement Supersonique Uniforme, or Reaction Kinetics in Uniform Supersonic Flow) apparatuses.

It is thought that long chain cyanopolyyne molecules H(C2)nCN may play an important role in the formation of the orange haze layer in Titan's atmosphere. 3 The longest carbon chain molecule observed in interstellar space, HC11N, is also a member of this series. Reactions of radicals such as CN, C2H and C3N with unsaturated hydrocarbons may provide an important route for the synthesis of cyanopolyynes in these low temperature environments. I will present our latest results on reactions of CN and C2H reactions with diacetylene and cyanoacetylene, 4 and compare them to fully ab-initio (two) transition state theory5 predictions based on new, highly accurate electronic structure calculations. I will also present our first results on the kinetics of C3N radical reactions, which can lead to the highly efficient incorporation of nitrogen into organic molecules via rapid reactions with small unsaturated -- and saturated -- hydrocarbons.

Low temperature kinetics and isomer resolved product branching ratios: Key inputs for photochemical models of planetary atmospheres

Kevin R. Wilson
Chemical Sciences
Lawrence Berkeley National Laboratory
Berkeley, CA 94720, United States

Reactions between organic free radicals and unsaturated hydrocarbons are important first steps in molecular growth, which ultimately leads to aerosol formation, a key feature of Titan's atmosphere. Low temperature branching ratios of radical-neutral reactions are key inputs for photochemical models of planetary atmospheres. However, there are currently very few experimental measurements of low temperature product branching ratios included in these models. At the Advanced Light Source at Lawrence Berkeley National Laboratory, a new apparatus has been developed, which combines a Laval expansion to study low temperature chemical reactions using time resolved photoionization mass spectrometry. Resulting photoionization spectra are used to derive low temperature isomer resolved product branching ratios for a set of key reactions. The latest results on a set of alkenes reacting with the ethynyl will be presented and the implications for Titan's chemistry will be discussed.

Reaction mechanisms of the growth of nitrogen-containing polycyclic aromatic compounds at low temperatures: A view from theoretical calculations of potential energy surfaces

Alexander Landera, Alexander M. Mebel
Department of Chemistry and Biochemistry
Florida International University
Miami, Florida 33199, United States

We overview recent results of high-level ab initio calculations of potential energy surfaces, combined with statistical calculations of product branching ratios, aimed to unravel reaction mechanisms of the growth of nitrogen-containing polycyclic aromatic compounds under low-temperature conditions. We show that ethynyl substituted 1- and 2-azanaphthalenes can be produced by consecutive CN and C2H additions to styrene or by two C2H additions to N-methylene-benzenamine. All CN and C2H radical addition complexes are formed in the entrance channels without barriers and the reactions are computed to be exothermic, with all intermediates and transition states along the favorable pathways residing lower in energy than the initial reactants. The reactions are completed by dissociation of chemically activated radical intermediates via H losses, so that collisional stabilization of the intermediates is not required to form final products. These features make the proposed mechanism viable even at very low temperatures and under single-collision conditions and especially significant for astrochemical environments. According to RRKM-ME calculations of reaction rate constants and product branching ratios at pressures from 3 to 10-6 mbar and temperatures of 90-200 K relevant to the organic aerosol formation regions in the stratosphere of a Saturn's moon Titan, collisional stabilization of the initial CN + styrene reaction adducts may be significant, but substantial amounts of 2-vinylbenzonitrile and 2-ethynyl-N-methylene-benzenamine can still be produced and then react with C2H to form substituted azanaphthalenes. The proposed mechanism is compared with consecutive CN and C2H additions to benzene occurring through the C2H-for-H and CN-for-H exchanges and leading first to the formation of 2-ethynyl-benzonitrile, the reaction of which with C2H may produce ethynyl-azanaphthyl radicals. These reactions are also feasible at low temperatures owing to their barrierless and exothermic character, but they can form ethynyl-azanaphthyl radicals as final products only under the conditions where collisional stabilization of these radicals is significant.

The planet Saturn

UV stimulated fluorescence studies of PAH-water ice mixtures

Rebecca Silva, Robert Hodyss, Paul V Johnson
Department of Chemistry and Environmental Science
University of Texas at Brownsville
Brownsville, TX 78520, United States

Planetary Ices Group
Jet Propulsion Laboratory
Pasadena, CA 91109, United States

A principal goal of astrobiology is to detect and inventory the population of organic compounds on extraterrestrial bodies. Targets of specific interest include the wealth of icy worlds that populate our Solar System. One potential technique for in situ detection of organics trapped in water ice matrices involves ultraviolet-stimulated emission from these compounds. Here, we report fluorescence spectra of a range of PAHs as pure solids and in water ice matrices at cryogenic temperatures. Matrix-isolated samples of polycyclic aromatic hydrocarbons (PAH) -- water ice mixtures are prepared by depositing PAH vapors effusing from a Knudsen cell simultaneously with water vapor onto an optical window at ~12K. Specifically, 248.6 nm stimulated UV fluorescence of naphthalene, anthracene, phenanthrene, pyrene, chrysene, and coronene, as pure solids and in water ice respectively, were studied at temperatures ranging from 12K to 125K. All fluorescence emissions were found to decrease in intensity with increasing temperature but not fully regain intensity when restored to 12K. The spectra PAH - water ice mixtures exhibited sharp peaks with ascending size, enabling extraction of characteristic vibrational frequencies from the fluorescence spectra.

New mechanisms for isotopic fractionation in the ISM: Observation of a strong 12C/13C isotope effect in the photochemical dissociation and desorption of CO2 (ice) by Lyman-a radiation

John T. Yates, Jr., Chunqing Yuan.
Department of Chemistry
University of Virginia
Charlottesville, Virginia 22904, United States

When electronically-excited molecules dissociate in an ice, quenching effects along the repulsive upper state potential energy curve will favor the production of the light isotopic fragment and its subsequent reaction in the ice. For CO2 (ice) at 75 K, we have shown that a 12C/13C enrichment effect of the order of 1.1 occurs for the production of reactive CO species which then go on to produce carbon trioxide, CO3. This effect in an ice is analogous to similar isotope enrichment effects well known for chemisorbed molecules on surfaces and has to do with the higher average velocity of the less massive departing fragment species in the region of electronic deexcitation.

Additionally, we show that vibrationally excited species of CO2, produced by the lattice-quenching effect on the photoproduced-excited state, can either vibrationally relax in the lattice or desorb from the lattice. The rate of vibrational relaxation is strongly governed by the interaction of the vibrationally-excited species with the lattice which may be tuned or detuned for efficient energy transfer by isotopic matching. The desorption rate of the molecule from the ice is inversely correlated with its ability to relax vibrationally in the ice lattice. This effect results in the enrichment of the majority isotopomer in the ice.

These two isotopic selection effects due to photochemical excitation of molecules in condensed media, possibly multiplied numerous times over astronomical time scales, suggest that the use of isotopic ratios in molecules in space for tracing their chemical history will have to consider these effects if the molecules have been subjected to photochemistry in condensed media.

Investigation of photochemistry of interstellar molecules using synchrotron VUV

Bing-Ming Cheng
Scientific Research Division
National Synchrotron Radiation Research Center
Hsinchu, Taiwan Republic of China

Photochemical and photophysical processes in condensed phases attract interest because information from these experiments yields detailed knowledge about chemical transformations in extraterrestrial invironments, insight into internal energy transfer and molecular dynamics, and new spectral data for transient species. To study the photochemistry of solid interstellar molecules, we have constructed a 3 K cryostat/FTIR end station coupled to a beam line of a synchrotron at National Synchrotron Radiation Research Center (NSRRC) in Taiwan. Upon excitation in situ of solid samples with light of tunable wave length generated with an electron synchrotron in the vacuum-ultraviolet (VUV) spectral region, the photochemical products were deduced from their absorption spectra in the mid infrared region, recorded, at each stage of an experiment, with an interferometric spectrometer. Taking the advantage of the unique property of synchrotron, we explore the spectroscopy of transient species and photochemistry of solid interstellar molecules with exciting prospects. In this work, infrared and ultraviolet spectra of solid interstellar molecules (e.g. N2, CH4, C2H2, and C2H4) and their photolysis products including the transient species will be presented, with a suggested mechanism of the photochemical and photophysical processes involving atomic and molecular free radicals. Our results contribute important data to improve our understanding of photochemical synthesis of prebiotic molecules via abiotic compounds in the interstellar medium and on icy surfaces of planets and satellites in the solar system.

Sugars and related compounds in residues produced from the UV irradiation of astrophysical ice analogs

Michel Nuevo, Scott A Sandford, George Cooper.
NASA Ames Research Center
Moffett Field, California 94035, United States

SETI Institute
Mountain View, California 94043, United States

A large variety and number of organic compounds of biological and prebiotic interests have been detected in meteorites, including sugars and other related compounds such as sugar acids1 . The presence of these compounds in meteorites, along with amino acids, amphiphiles, and nucleobases, strongly suggests that molecules essential to life can be formed abiotically under astrophysical conditions. The formation of amino acids2-4 , amphiphiles5 , nucleobases6,7 , as well as other organic compounds8,9 from the ultraviolet (UV) irradiation of astrophysical ice analogs has been extensively studied in the laboratory. However, until now there was no reported search for the presence of sugars, sugar alcohols, sugar acids, and sugar diacids in laboratory residues, and only a few small 3-carbon sugar derivatives such as glycerol and glyceric acid have been detected in such organic residues8 . In this study, we show prelimary results of the search for sugars and sugar-related compounds in organic residues produced from the UV irradiation of astrophysical ice analogs, and compare our experimental data with measurements of these compounds in primitive meteorites.

State specific non-adiabatic branching ratios for N2 and CO using tunable VUV lasers and time-sliced velocity-map ion imaging for detection

William M. Jackson, Yu Song, Hong Gao, Cheuk Ng.
Chemistry, University of California Davis
CA 95616, United States

Two independently tunable VUV laser sources are combined with a time-sliced velocity-map ion imaging, VMII, detection system to study the state-selected photodissociation dynamics of N2 and CO. Resonant nonlinear four-wave sum-frequency (2ω1 + ω 2 ) mixing, RFWM, using a rare gas jet as the nonlinear medium is used to produce the tunable VUV laser sources. The ω1 and ω2 are the UV and visible laser frequencies, respectively. This RFWM method produces enough intensity so that unfocused laser light may be used with VMII detection to determine the product branching ratio and recoil anisotropy parameters as a function of the ro-vibronic level of parent molecules. Three dissociation channels of N2, namely, the N(4S) + N(2D), N(4S) + N(2P) and N(2D) + N(2D) are studied in the energy region between 12.50-15.15 eV. For CO in the same energy region, the branching ratio between the spin-allowed C(3PJ) + O(3PJ) and the spin-forbidden C(1D) + O(3PJ) and C(3PJ) + O(1D) channels are measured. The areas in astrochemistry that can be affected by the increased reactivity of the metastable atoms that are produced by these molecules will be discussed.

Size comparison of Saturn and Earth

Electronic structure calculations for understanding the association and growth of small carbon clusters

Martin Head-Gordon, Roberto Peverati, Partha P Bera, Timothy J. Lee.
Department of Chemistry
University of California, Berkeley
CA 94720, United States

Space Science & Astrobiology Division
NASA Ames Research Center
Moffett Field, CA 94035, United States

A rich variety of open shell molecules and ions are known in the interstellar medium. Many such species are "electronically frustrated" in the sense that they have incomplete valence shells, and can therefore interact much more strongly with other molecules or even atoms that they may encounter than would a stable closed shell species. In this talk, I shall discuss electronic structure calculations on several model complexes that are relevant to laboratory experiments. As a backdrop to those calculations, I shall briefly review methods for unraveling intermolecular interactions, with an emphasis on those involving radicals.

The objective is to examine a range of novel encounter complexes and the intermolecular interactions that make them stable via electronic structure theory. One such example is the association of the radical cations of acetylene and ethylene with their neutral parents. The resulting encounter complexes are formed without barriers, and exhibit remarkable intermolecular interactions, which are discussed. Other examples that are relevant to carbon particle growth in the interstellar medium will be discussed, including the formation process for other C4 carbocations that have been experimentally observed in plasmas formed from acetylene and ethylene feeds.

Role of benzene photolysis in Titan haze formation

Y. Heidi Yoon, Sarah M. Horst, Raea K. Hicks, Rui Li1, Joost A. de Gouw1, Margaret A. Tolbert.
Cooperative Institute for Research in Environmental Sciences
Boulder, CO 80309, United States

Department of Chemistry and Biochemistry
University of Colorado-Boulder
Boulder, CO 80309, United States

NOAA Earth System Research Laboratory
Boulder, CO 80305, United States

Since the arrival of the Cassini spacecraft to the Saturnian system, benzene (C6H6) has been observed throughout Titan's atmosphere. Photochemical reactions involving benzene may influence polycyclic aromatic hydrocarbon formation, aerosol formation, and the radiative balance of planetary atmospheres. We study the chemistry of benzene in the laboratory by photolyzing CH4/N2 gas mixtures infused with ppm-levels of C6H6 using a deuterium lamp (115-400 nm). We measure the chemical composition of the condensed and gas-phase products in situ using aerosol mass spectrometry and proton-transfer ion-trap mass spectrometry, respectively. Inclusion of benzene significantly increases the total gas-phase products found and increases the aromaticity of the resultant gases. The addition of benzene also increases aerosol production, but decreases nitrogen incorporation into aerosol. The aerosol formation is also studied as a function of pressure, and we find that as the pressure decreases, the C/H ratio of the condensed phase products increases and the N/C ratio decreases.

Novel experimental approaches for fundamental studies of laboratory astrochemistry

Arthur Suits, Bernadette M. Broderick, Yumin Lee, James Oldham, Kirill Prozument, Chamara Abeysekara, Barratt Park, Robert W. Field.
Department of Chemistry
Wayne State University
Detroit, MI 48202, United States

Massachusetts Institute of Technology
Cambridge, MA 02139, United States

Two novel techniques enabling diverse probes of the chemistry of the atmospheres of outer planets are being developed in our laboratories. The study of spin-polarized hydrogen atoms which result from photodissociation of molecules offers a powerful new means of unraveling complex photochemical processes in polyatomic molecules. Examination of the detailed speed-dependent H-atom spin polarization is achieved by determining the projection of the electron spin onto the probe laser direction. In doing so, its angular distribution, complex dissociation pathways, and coherent excitation mechanisms may be revealed. Here we have adapted the H atom Rydberg tagging technique with its extraordinary velocity resolution to give the velocity-dependent H atom spin polarization. The methodology described herein serves as a general probe of multi-surface nonadiabatic dynamics, sensitive to coherent effects in dissociation along multiple paths, and is applicable to a wide range of astrochemically-relevant polyatomic systems.

A second approach, Chirped-pulse Fourier-Transform Millimeter Wave Spectroscopy, has revolutionized broadband rotational spectroscopy with vastly reduced acquisition times, with further sensitivity possible when more molecules can interact with the microwave field. We hae developed a high-power mmWave system that incorporates a pulsed Laval flow to produce a uniform supersonic flow, yielding thermalized reactants at a high density and high volume yet low rotational temperature. It thus provides the ideal extension of the CP-FTMW technique for studying chemical reactions. This combination promises a method of near universal application that quantitatively detects nascent product isomers and conformers with vibrational level specificity. This will be suitable for a wide range of applications in reaction dynamics studies, including combustion-, atmospheric-, and astrochemistry.

Huygens probe used to study Titan
Organic chemistry in the Kronian satellite system: Titan and Enceladus

Jack Hunter Waite, Timothy Brockwell, Brian Magee, Benjamin Teolis, Joseph Westlake.
Space Science and Engineering
Southwest Research Institute
San Antonio, Texas 78228, United States

Space Science
Johns Hopkins Applied Physics Laboratory
Laurel, Maryland 20723, United States

This paper will present the Cassini Ion Neutral Mass Spectrometer findings on the composition and structure of the upper atmosphere of Titan and the Enceladus cryo-geyser. Challenges of performing mass spectrometry in the harsh environment of space will be discussed. Emphasis will be placed on the rich organic chemistry found at both Titan and Enceladus. The two chemistries will be compared and contrasted with respect to origin and evolution. Ion neutral chemistry taking place in the upper atmosphere of Titan will be presented including the roll of neutral, positive ion, and negative ion and their interplay to produce complex organic compounds exceeding 5000 u.

Theoretical kinetics as a tool for exploring the chemistry of Titan's atmosphere

Stephen J Klippenstein, Veronique Vuitton, Roger V Yelle, Sarah M Horst, Panayotis Lavvas, Axel Bazin.
Chemical Sciences and Engineering Division
Argonne National Laboratory
Argonne, IL 60439, United States

Institut de Planetologie et d'Astrophysique de Grenoble
UJF-Grenoble 1/CNRS-INSU, UMR 5274, Grenoble, France

Lunar and Planetary Laboratory
University of Arizona
Tucson, AZ 85721, United States

Cooperative Institute for Research in Environmental Sciences
University of Colorado
Boulder, CO 80309, United States

Groupe de Spectrometrie Moleculaire et Atmospherique
Universite Reims Champagne-Ardenne/CNRS
UMR 6089, Reims, France

We will illustrate the contribution of theoretical kinetics studies to the resolution of various aspects of the chemistry in Titan's atmosphere. Predictions for the temperature dependence of the branching ratios in the reaction of CH3 with OH and of 1CH2 with H2O help to understand the conversion of OH/H2O to CO. A study of the H2CN + H reaction helps understand the production of HNC, while studies of the N(2D) + HNC and H + HNC reactions help understand its loss. A study of the C2H3 + HCN reaction suggests a significantly decreased rate of production for C2H3CN. A study of CH3 + HCNH+ helps to understand the loss of HCNH+. Studies of HCNH+ with HCN and with HC3N help to understand the role of proton bound dimers.

Imaging ion-molecule reactions: Applications in astrochemistry

Linsen Pei, James M. Farrar.
Department of Chemistry
University of Rochester
Rochester, NY 14627, United States

Ion-molecule reactions are of critical importance in initiating ion processing in the atmosphere of Titan. Specifically, the reactions of N+ and N2+ with CH4 are of central importance to the ion chemistry of Titan. The N+ reactant may undergo both dissociative and non-dissociative charge transfer with CH4, as well as C-N bond formation to produce HCNH+, and each set of reaction products plays a unique role in the subsequent ion chemistry. Facile insertion of N+into C-H bonds of CH4 to form chemically activated ions that decay by ejection of hydrogen atoms or molecules leads to the formation of HCNH+, which may serve as proton donor to a number of species. Careful measurements of kinetic energy distributions in this system provide important insight into the spin-forbidden and spin-allowed pathways accessible in the formation of reaction products. The N2+ reactant only undergoes dissociative charge transfer reactions with CH4. These studies address the complementary and competitive roles that energy resonance and favorable Franck-Condon factors play in charge transfer, where ionization of CH4 results in extensive changes in geometry. We employ the Velocity Map Imaging method to the detection of reaction products of low energy ion-molecule collisions studied in crossed beams. By crossing a mass-selected ion beam with a pulsed neutral molecular beam, delayed pulsed extraction of product ions from the interaction region allows us to determine energy and angular distributions of reaction products over a range of collision energies. The experimental results, in concert with Gaussian G2 calculations, provide a detailed picture of reaction pathways, reactive intermediate lifetimes, and energy disposal in ionic reactions important in astrochemistry.

Dissociation of the CO2 and C2H2 molecular dications: Their role in the upper atmospheres of planets

Stefano Falcinelli, Marzio Rosi, Pietro Candori, Franco Vecchiocattivi, Fernando Pirani, Nadia Balucani, Michele Alagia, Robert Richter, Stefano Stranges.
Department of Civil and Environmental Engineering
University of Perugia
Perugia, PG 06125, Italy

Institute of Molecular Science and Technologies (ISTM) CNR
Perugia, PG 06123, Italy

Department of Chemistry
University of Perugia
Perugia, PG 06123, Italy

Tecnologie Avanzate e Nanoscienza (TASC) Laboratory, IOM CNR
Trieste, Italy

Area Science Park, Sincrotrone Trieste
Basovizza, Trieste 34149, Italy

Department of Chemistry
University of Rome 'La Sapienza'
Rome, Italy

The double dissociative photoionization of CO2 and C2H2 molecules has been studied by using synchrotron radiation in the 34-50 eV photon energy range and detecting electron-ion and electron-ion-ion coincidences. The experiments have been carried out at the synchrotron light laboratory ELETTRA (Trieste, Italy). These processes are of interest because of the involvement of CO2 and C2H2 in several atmospheric phenomena of the Earth and of other planets and in plasma environments. For example, in Mars' atmosphere, where CO2 is the main component, the importance of the CO22+ dication and its dissociation has been recently demonstrated. In the case of CO2, three processes have been observed: (i) the formation of the CO22+ molecular dication, (ii) the production of a metastable (CO22+)* that dissociates, with an apparent lifetime of 3.1 μs, giving rise to CO+ and O+ ions, and (iii) the dissociation leading to the same products, but occurring with a lifetime shorter than 0.05 μs. At low photon energy, the CO+ and O+ product ions separate predominantly with a total kinetic energy release (KER) between 3 and 4 eV. This mechanism becomes gradually less important when the photon energy increases and, at 49 eV, a process where the two products separate with a KER between 5 and 6 eV is dominant. In the case of acetylene, the dissociation leading to C2H++H+ products occurs through a metastable dication with a lifetime of 108±22 ns, and a KER of about 4.3 eV. The reaction leading to CH2++C+ occurs in a time shorter than the typical rotational period of the acetylene molecules (of the order of 10−12 s) with a KER of ∼4.5 eV. The symmetric dissociation, leading to CH++CH+, exhibits a KER distribution with a maximum at ∼5.2 eV.

Stimulated formation of CO2 at buried ice: Graphite grain interfaces

Thomas Michael Orlando, Jiaming Shi, Gregoary A. Greives.
School of Chemistry and Biochemistry
Georgia Institute of Technology
Atlanta, Georgia 30318, United States

The VUV synthesis of CO2 on ice-coated graphite grain interfaces has been examined from 40 to 120 K. CO2 forms at the buried water graphite interface and this process likely contributes to the CO2 reservoir in dense clouds. The photosynthesized CO2 molecules will also desorb in hot photon dominated regions and lost to space when the VUV processed ice coated carbonaceous grains cycle within the proto-planetary disk. Thus, VUV stimulated reactions at buried carbon grain interfaces may contribute to the carbon deficit of Earth relative to comets and meteorites.

Formation of high mass hydrocarbons on hydrocarbon astrophysical ice analogs

Brant Jones, Ralf Kaiser.
Department of Chemistry
University of Hawaii at Manoa
Honolulu, HI 96822, United States

We present recent results from the newly established W.M. Keck Research Laboratory in Astrochemistry regarding the formation of high molecular weight (~ C22) hydrocarbons starting from pure, simple hydrocarbons ices upon interaction of these ices with ionizing radiation. Specifically, we have utilized for the very first time a novel application of reflection time-of-flight mass spectrometry (ReTOF) coupled with soft vacuum ultraviolet photoionization to observe the high mass hydrocarbons synthesized following energetic processing and thermal desorption as a function of their respective sublimation temperature. Simple hydrocarbons such as methane have been detected on the surfaces of icy bodies in the outer Solar System objects and in dense molecular clouds. The surfaces of these bodies have undergone millions (cold molecular clouds) to billions of years (airless Solar System bodies) of chemical processing due to ionizing radiation from the solar wind and Galactic Cosmic Radiation. Our research has been focused on trying to understand how these ices have evolved by simulating the chemical processing via ionizing radiation in an ultrahigh vacuum chamber utilizing a variety of optical analytical spectroscopies (FT-IR, Raman, UV-Vis) and gas phase mass spectroscopy. In particular, results from ReTOF spectroscopy with soft vacuum ultraviolet photoionization of the subliming neutral products at Ehv = 10.5 eV indicate that over 50 molecules with distinct m/z ratios and sublimation temperatures are formed easily under conditions relevant to a plethora of astrophysical icy environments. Despite, the numerous previous experimental investigations probing the effect of ionizing radiation on simple hydrocarbon astrophysical ice analogs, our results suggest that there is still a vast quantity of knowledge to be had and we now have the ability to probe further into a door that may have been prematurely closed.

Irradiation of solid water ice-carbon dioxide mixtures with 100 keV protons

Ujjwal Raut, Raul A Baragiola.
Laboratory for Atomic and Surface Physics
Material Science and Engineering
University of Virginia, Charlottesville, VA 22904-4745, United States

Recent detection of CO2-O2 exospheres around Saturnian satellites (1) presents an interesting puzzle. The O2 can be generated from radiolysis of water ice on the surface, a process that is fairly well understood. The CO2, detected in nearly equal amounts as O2, is surprising since (i) there is no evidence of endogenic CO2 source on these satellites (ii) there is little CO2 on the surface of these satellites; water ice is the dominant constituent (~ 99%) according to Cassini's Infrared Spectrometer (2) and (iii) our recent studies on ion irradiation of pure solid CO2 films show that CO and O2 are the major constituents of the sputtered flux (3).

At this meeting, we will present results in sputtering and radiation chemistry of water-carbon dioxide mixtures of various mixing ratios, comparing these results with our previous study of pure CO2. We will also irradiate water ice films in presence of ambient gas-phase CO2 in an attempt to closely simulate the conditions at the moons of Saturn. The results from these experiments, specially the sputtering rates of different species, will be directly relevant to the CO2 detection in the exosphere of the satellites.

THz time-domain spectroscopy of interstellar ice analogs

Sergio Ioppolo, Marco A Allodi, Brett A McGuire, Matthew J Kelley, Geoffrey A Blake.
Division of Geological and Planetary Sciences
Pasadena, California 91125, United States

Division of Chemistry and Chemical Engineering
Pasadena, California 91125, United States

International astronomical facilities, in particular the Herschel Space Telescope, SOFIA and ALMA, are currently characterizing the interstellar medium (ISM) by collecting a huge amount of new THz spectral data that must be compared to THz laboratory spectra to be interpreted. The latter, however, are largely lacking, and this severely restricts the scientific impact of the astronomical observations. We have recently constructed a new THz time-domain spectroscopy system to investigate the spectra of interstellar relevant ice analogs in the range between 0.3-7 THz. The system is coupled to a FT-IR spectrometer to monitor the ices in the mid-IR (4000 - 500 cm-1). This talk will focus on the laboratory investigation of the composition and structure of the bulk phases of interstellar ice analogs (i.e., H2O, CO2, CO, CH3OH, NH3, CH4). The ultimate goal of this research project is to provide the scientific community with an extensive THz ice-database, which will allow quantitative studies of the ISM, and guide future astronomical observations of species in the solid phase.

Laser desorption, molecular beams, and synchrotron radiation for analysis of complex organic matter

Musahid Ahmed
Chemical Sciences Division
Lawrence Berkeley National Laboratory
Berkeley, CA 94720, United States

Tunable vacuum ultraviolet radiation generated at a synchrotron provides a universal, yet selective scalpel to decipher molecular information in complex chemical systems when coupled to mass spectrometry. Here we will showcase some of our recent results in identifying plant and microbial components in soil organic matter, the chemical composition of melanin in extant and fossil bird feathers, and decomposition and fragmentation of sugars and alcohols of relevance to astrochemistry. We will discuss how chemical analysis can be performed by using electronic structure methods in conjunction with photoionization and fragmentation dynamics.

On the use of microfluidic chemical and biochemical analysis devices to detect dipeptides synthesized in interstellar model ices

Richard A Mathies1, Ralf I. Kaiser, Amanda Stockton, Yong S. Kim, Erik Jensen.
Department of Chemistry
University of California, Berkeley
Berkeley, CA 94720, United States

Department of Chemistry
University of Hawaii at Manoa
Honolulu, HI 96822, United States

Jet Propulsion Laboratory
California Institute of Technology
Pasadena, CA 01109, United States

The detection of chemical biomarkers that provide data on the origin of life or that are signatures of extinct or extant life elsewhere in the solar system, depends on the development of methods and apparatus that can detect a wide variety of chemical/biochemical species, that can be integrated into portable analyzers, and that have the sensitivity actually needed to detect trace biomarker residues. We have focused on microfluidic technology because it provides the unique ability to develop chemical analysis systems for sample processing, labeling and high sensitivity detection that are both small and robust enough for space exploration. Thus we developed the Mars Organic Analyzer, which demonstrated high sensitivity detection of amino acids both in the lab and in the barren Atacama Desert. In subsequent work, the sensitivity was increased using Pacific Blue labeling making this system the most sensitive analytical device for detecting organic amines and amino acids and the utility was increased further by developing automated chemical methods for analyzing aldehydes, ketones, carboxylic acids, and polycyclic aromatic hydrocarbons.

To demonstrate the capabilities of the MOA, we recently completed a collaborative experiment with the Kaiser Group in Hawaii examining interstellar ice models made up of CO2, NH3, and hydrocarbons that have been irradiated with high energy electrons that simulate galactic cosmic rays. Irradiation under UHV conditions at 10 K induces amide bond-like IR absorption features in the sample films; subsequent extraction, labeling and analysis with the MOA demonstrates that amino acids and at least Gly-Gly and Leu-Ala dipeptides are formed in quantities that can be readily detected by the MOA. This work suggests that, once produced, extraterrestrial polypeptides could have inseminated early Earth via comets and meteorites and catalyzed its biological evolution. See Kaiser, R. I, et al., Astrophysical Journal. 765 :111, March 10, 2013.

UV photoprocessing of interstellar ice analogs

E.C. Fayolle1, M. Bertin, C. Romanzin, H.A.M. Poderoso, X. Michaut, A. Moudens, L. Philippe, P. Jeseck, K.I. Oberg, H. Linnartz, J.-H. Fillion.
Leiden Observatory
University of Leiden
Leiden, The Netherlands

Laboratoire de physique moléculaire pour l’atmosphère et l’astrophysique (LPMAA)
UPMC - Univ. Paris 6
Paris, France

Laboratoire de Chimie Physique (LCP)
Univ. Paris Sud 11
Paris, France

Department Chemistry and Astronomy
Univ. of Virginia
Charlottesville, United States

UV photoprocessing of icy dust grains induces desorption and dissociation. Photodesorption offers a non-thermal mechanism that is relevant to explain the gas-to-ice balance observed for small molecules. Photodissociation produces radical species that desorb from or diffuse over the ice surface, reacting with other species and participating in solid state reactions that offer pathways towards molecular complexity. Studies of these fundamental processes in the past have been performed using broadband (microwave driven H2 discharge) lamps peaking around 10.2 eV (Ly-a). Using also monochromatic vacuum UV light, available from the beamline DESIRS at the synchrotron facility SOLEIL, it is also possible to resonantly excite specific solid state processes. This provides detailed and valuable information on the underlying molecular mechanisms.

This talk reviews recent experiments that focus on wavelength dependent photodesorption of CO, N2, O2, and water. It discusses the potential role of co-desorption, illustrates the role water plays in the ice upon vacuum UV irradiation, and presents the idea of a (partially) wavelength dependent chemistry in space.

Amino acids in carbonaceous chondrites and potential formation mechanisms

Jamie E. Elsila, Aaron S. Burton, Michael P. Callahan, Jason P. Dworkin, Daniel P. Glavin.
Solar System Exploration Division
NASA Goddard Space Flight Center
Greenbelt, MD 20771, United States

Carbonaceous chondrites are primitive stony meteorites that contain a diverse suite of soluble organic compounds, among them a variety of amino acids. The abundances, structural distributions, and stable isotopic ratios of these compounds reflect their synthesis and evolutionary history. Amino acid compositions vary between the different carbonaceous chondrite groups, with thermally altered CV and CO chondrites showing distinct differences from the more aqueously altered CM, CI, and CR chondrites as well as from the metal-rich CH and CB chondrites. Here, we report on the differences in structural distributions and isotopic compositions between amino acids in these chondrite groups, and show how these differences may result from the activation of different formation mechanisms depending on meteorite parent body conditions.

Millimeter- and submillimeter-wave spectroscopy of species of astrophysical importance

Luca Dore
Department of Chemistry "Giacomo Ciamician"
University of Bologna
Bologna, Italy

During the last decades the development of millimeter-wave and infrared astronomy has enabled a detailed exploration of the cold universe. Spectral lines of over 170 molecules and radicals have been assigned which allow to probe the physics and chemistry of interstellar clouds and regions of star formation. The unprecedented sensitivity of current observations raised a new problem, i.e., the detection of many unidentified signals, which represent a large fraction of the detected lines. This means that precious pieces of information still need to be disclosed. In order to assign these unidentified features, laboratory studies are required.

Measurements carried out in Bologna with a source-modulation microwave spectrometer equipped either with a cell coupled to a pyrolysis apparatus or a DC-discharge cell will be presented. The molecular species investigated include imines, molecular ions, deuterated diacetylene, substituted acetylene.

In addition, after the laboratory detection of the submillimeter-wave spectrum of the 15N-containing isotopologues of N2H+, the 15NNH+ (1-0) and N15NH+ (1-0) lines were detected in the starless cloud core L1544. This allows to discuss the 15N fractionation of N2H+ in the interstellar gas.

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