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  • 51.
    Vigren, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Hamberg, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Danielsson, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    Semaniak, Jacek
    Andersson, Patrik U.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Dissociative recombination of fully deuterated protonated acetonitrile, CD3CND+: Product branching fractions, absolute cross section and thermal rate coefficient2008In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 10, no 27, p. 4014-4019Article in journal (Refereed)
    Abstract [en]

    The dissociative recombination of fully deuterated protonated acetonitrile, CD3CND+, has been investigated at the CRYRING heavy ion storage ring, located at the Manne Siegbahn Laboratory, Stockholm, Sweden. Branching fractions were measured at similar to 0 eV relative collision energy between the ions and the electrons and in 65% of the DR events there was no rupture of bonds between heavy atoms. In the remaining 35%, one of the bonds between the heavy atoms was broken. The DR cross-section was measured between similar to 0 eV and 1 eV relative collision energy. In the energy region between 1 meV and 0.1 eV the cross section data were best fitted by the expression sigma = 7.37 x 10(-16) (E/eV)(-1.23) cm(2), whereas sigma = 4.12 x 10(-16) (E/eV)(-1.46) cm(2) was the best fit for the energy region between 0.1 and 1.0 eV. From the cross section a thermal rate coefficient of alpha(T) = 8.13 x 10(-7) (T/300)(-0.69) cm(3) s(-1) was deduced.

  • 52.
    Vigren, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Hamberg, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Semaniak, Jacek
    Danielsson, Mathias
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Dissociative recombination of the deuterated acetaldehyde ion, CD3CDO+: product branching fractions, absolute cross sections and thermal rate coefficient2007In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 9, no 22, p. 2856-2861Article in journal (Refereed)
    Abstract [en]

    Dissociative recombination of the deuterated acetaldehyde ion CD3CDO+ has been studied at the heavy-ion storage ring CRYRING, located at the Manne Siegbahn Laboratory, Stockholm, Sweden. Product branching fractions together with absolute DR cross-sections were measured. The branching fractions were determined at a relative collision energy between the ions and the electrons of 0 eV. With a probability of 34% the DR events resulted in no ruptures of bonds between heavy atoms (i.e. no breakage of the C–C bond or the CO bond). In the remaining 66% of the events one of the bonds between the heavy atoms was broken. The energy-dependent cross-section for the DR reaction was measured between 0 and 1 eV relative kinetic energy. In the energy region between 1 meV and 0.2 eV the absolute cross section could be fitted by the expression σ(E) = 6.8 × 10−16E−1.28 cm2, whereas in the energy interval between 0.2 and 1 eV the data were best fitted by σ(E) = 4.1 × 10−16E−1.60 cm2. From these cross section data the thermal rate coefficient (as a function of the electron temperature), α(T) = 9.2 × 10−7 (T/300)−0.72 cm3 s−1 was obtained.

  • 53.
    Vigren, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Semaniak, J.
    Hamberg, M.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, V.
    Kaminska, M.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Dissociative recombination of nitrile ions with implications for Titan's upper atmosphere2012In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 60, no 1, p. 102-106Article in journal (Refereed)
    Abstract [en]

    Nitrile ions are abundant in Titan's upper atmosphere and are expected to be lost mainly via dissociative recombination with free electrons. We review in this paper a series of experimental results on the dissociative recombination reactions of nitrile ions known/expected to be present in Titan's upper atmosphere. The experiments were all performed at the heavy ion storage ring CRYRING in Stockholm, Sweden, and the results presented here include information on rate coefficients at electron temperatures relevant for Titan's upper atmosphere as well as information on the product branching fractions of the reactions. We discuss implications of the results for Titan's atmosphere. As an example the presented results support a statement by Krasnopolsky (2009) that nitriles do not degrade to yield N-2 again in Titan's atmosphere, indicating that condensation and polymerization with precipitation to the surface are their ultimate fate.

  • 54.
    Vigren, Erik
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Zhaunerchyk, Vitali
    Stockholm University, Faculty of Science, Department of Physics.
    Hamberg, M.
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, M.
    Semaniak, J.
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Reassessment of the dissociative recombination of n2h+ at cryring2012In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 757, no 1, p. 34-Article in journal (Refereed)
    Abstract [en]

    The dissociative recombination (DR) of N2H+ has been reinvestigated at the heavy ion storage ring CRYRING at the Manne Siegbahn Laboratory in Stockholm, Sweden. Thermal rate coefficients for electron temperatures between 10 and 1000 K have been deduced. We show that electron recombination is expected to play an approximately equally important role as CO in the removal of N2H+ in dark interstellar clouds. We note that a deeper knowledge on the influence of the ions' rotational temperature in the DR of N2H+ would be helpful to set further constraints on the relative importance of the different destruction mechanisms for N2H+ in these environments. The branching fractions in the DR of N2H+ have been reinvestigated at similar to 0 eV relative kinetic energy, showing a strong dominance of the N-2 + H production channel (93(-2)(+4)%) with the rest leading to NH + N. These results are in good agreement with flowing afterglow experiments and in disagreement with an earlier measurement at CRYRING.

  • 55. Wakelam, V.
    et al.
    Herbst, E.
    Loison, J. -C
    Smith, I. W. M.
    Chandrasekaran, V.
    Pavone, B.
    Adams, N. G.
    Bacchus-Montabonel, M. -C
    Bergeat, A.
    Beroff, K.
    Bierbaum, V. M.
    Chabot, M.
    Dalgarno, A.
    van Dishoeck, E. F.
    Faure, A.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Gerlich, D.
    Galli, D.
    Hebrard, E.
    Hersant, F.
    Hickson, K. M.
    Honvault, P.
    Klippenstein, S. J.
    Le Picard, S.
    Nyman, G.
    Pernot, P.
    Schlemmer, S.
    Selsis, F.
    Sims, I. R.
    Talbi, D.
    Tennyson, J.
    Troe, J.
    Wester, R.
    Wiesenfeld, L.
    A KINETIC DATABASE FOR ASTROCHEMISTRY (KIDA)2012In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 199, no 1, p. 21-Article in journal (Refereed)
    Abstract [en]

    We present a novel chemical database for gas-phase astrochemistry. Named the KInetic Database for Astrochemistry (KIDA), this database consists of gas-phase reactions with rate coefficients and uncertainties that will be vetted to the greatest extent possible. Submissions of measured and calculated rate coefficients are welcome, and will be studied by experts before inclusion into the database. Besides providing kinetic information for the interstellar medium, KIDA is planned to contain such data for planetary atmospheres and for circumstellar envelopes. Each year, a subset of the reactions in the database (kida.uva) will be provided as a network for the simulation of the chemistry of dense interstellar clouds with temperatures between 10 K and 300 K. We also provide a code, named Nahoon, to study the time-dependent gas-phase chemistry of zero-dimensional and one-dimensional interstellar sources.

  • 56. Wakelam, V.
    et al.
    Loison, J.-C
    Herbst, E.
    Pavone, B.
    Bergeat, A.
    Beroff, K.
    Chabot, M.
    Faure, A.
    Galli, D.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Gerlich, D.
    Gratier, P.
    Harada, N.
    Hickson, K. M.
    Honvault, P.
    Klippenstein, S. J.
    Le Picard, S. D.
    Nyman, G.
    Ruaud, M.
    Schlemmer, S.
    Sims, I. R.
    Talbi, D.
    Tennyson, J.
    Wester, R.
    The 2014 KIDA Network for Interstellar Chemistry2015In: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 217, no 2, article id 20Article in journal (Refereed)
    Abstract [en]

    Chemical models used to study the chemical composition of the gas and the ices in the interstellar medium are based on a network of chemical reactions and associated rate coefficients. These reactions and rate coefficients are partially compiled from data in the literature, when available. We present in this paper kida.uva.2014, a new updated version of the kida.uva public gas-phase network first released in 2012. In addition to a description of the many specific updates, we illustrate changes in the predicted abundances of molecules for cold dense cloud conditions as compared with the results of the previous version of our network, kida.uva.2011.

  • 57. Wakelam, V.
    et al.
    Smith, I. W. M.
    Herbst, E.
    Troe, J.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Linnartz, H.
    Oeberg, K.
    Roueff, E.
    Agundez, M.
    Pernot, P.
    Cuppen, H. M.
    Loison, J. C.
    Talbi, D.
    Reaction Networks for Interstellar Chemical Modelling: Improvements and Challenges2010In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 156, no 04-jan, p. 13-72Article, review/survey (Refereed)
    Abstract [en]

    We survey the current situation regarding chemical modelling of the synthesis of molecules in the interstellar medium. The present state of knowledge concerning the rate coefficients and their uncertainties for the major gas-phase processes-ion-neutral reactions, neutral-neutral reactions, radiative association, and dissociative recombination-is reviewed. Emphasis is placed on those key reactions that have been identified, by sensitivity analyses, as 'crucial' in determining the predicted abundances of the species observed in the interstellar medium. These sensitivity analyses have been carried out for gas-phase models of three representative, molecule-rich, astronomical sources: the cold dense molecular clouds TMC-1 and L134N, and the expanding circumstellar envelope IRC +10216. Our review has led to the proposal of new values and uncertainties for the rate coefficients of many of the key reactions. The impact of these new data on the predicted abundances in TMC-1 and L134N is reported. Interstellar dust particles also influence the observed abundances of molecules in the interstellar medium. Their role is included in gas-grain, as distinct from gas-phase only, models. We review the methods for incorporating both accretion onto, and reactions on, the surfaces of grains in such models, as well as describing some recent experimental efforts to simulate and examine relevant processes in the laboratory. These efforts include experiments on the surface-catalyzed recombination of hydrogen atoms, on chemical processing on and in the ices that are known to exist on the surface of interstellar grains, and on desorption processes, which may enable species formed on grains to return to the gas-phase.

  • 58. Wirström, E. S.
    et al.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Hjalmarson, A.
    Persson, C. M.
    Black, J. H.
    Bergman, P.
    Millar, T. J.
    Hamberg, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    Vigren, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Observational tests of interstellar methanol formation2011In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 533, p. A24-Article in journal (Refereed)
    Abstract [en]

    Context. It has been established that the classical gas-phase production of interstellar methanol (CH(3)OH) cannot explain observed abundances. Instead it is now generally thought that the main formation path has to be by successive hydrogenation of solid CO on interstellar grain surfaces. Aims. While theoretical models and laboratory experiments show that methanol is efficiently formed from CO on cold grains, our aim is to test this scenario by astronomical observations of gas associated with young stellar objects (YSOs). Methods. We have observed the rotational transition quartets J = 2(K) - 1(K) of (12)CH(3)OH and (13)CH(3)OH at 96.7 and 94.4 GHz, respectively, towards a sample of massive YSOs in different stages of evolution. In addition, the J = 1-0 transitions of (12)C(18)O and (13)C(18)O were observed towards some of these sources. We use the (12)C/(13)C ratio to discriminate between gas-phase and grain surface origin: If methanol is formed from CO on grains, the ratios should be similar in CH(3)OH and CO. If not, the ratio should be higher in CH(3)OH due to (13)C fractionation in cold CO gas. We also estimate the abundance ratios between the nuclear spin types of methanol (E and A). If methanol is formed on grains, this ratio is likely to have been thermalized at the low physical temperature of the grain, and therefore show a relative over-abundance of A-methanol. Results. We show that the (12)C/(13)C isotopic ratio is very similar in gas-phase CH(3)OH and C(18)O, on the spatial scale of about 40 '', towards four YSOs. For two of our sources we find an overabundance of A-methanol as compared to E-methanol, corresponding to nuclear spin temperatures of 10 and 16 K. For the remaining five sources, the methanol E/A ratio is less than unity. Conclusions. While the (12)C/(13)C ratio test is consistent with methanol formation from hydrogenation of CO on grain surfaces, the result of the E/A ratio test is inconclusive.

  • 59. Yang, B.
    et al.
    Novotny, O.
    Krantz, C.
    Buhr, H.
    Mendes, M.
    Nordhorn, C.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Grieser, M.
    Repnow, R.
    Berg, M.
    Bing, D.
    Domesle, C.
    Grussie, F.
    Savin, D. Wolf
    Schwalm, D.
    Cai, X.
    Wolf, A.
    Exploring high-energy doubly excited states of NH by dissociative recombination of NH+2014In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 47, no 3, p. 035201-Article in journal (Refereed)
    Abstract [en]

    We have investigated electron capture by NH+ resulting in dissociative recombination (DR). The impact energies studied of similar to 4-12 eV extend over the range below the two lowest predicted NH+ dissociative states in the Franck-Condon (FC) region of the ion. Our focus has been on the final state populations of the resulting N and H atoms. The neutral DR fragments are detected downstream of a merged electron and ion beam interaction zone in the TSR storage ring, which is located at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany. Transverse fragment distances were measured on a recently developed high count-rate imaging detector. The distance distributions enabled a detailed tracking of the final state populations as a function of the electron collision energy. These can be correlated with doubly excited neutral states in the FC region of the ion. At low electron energy of similar to 5 eV, the atomic product final levels are nitrogen Rydberg states together with ground-state hydrogen. In a small electron energy interval near 7 eV, a significant part of the final state population forms hydrogen Rydberg atoms with nitrogen atoms in the first excited (D-2) term, showing the effect of Rydberg doubly excited states below the predicted 2(2)Pi ionic potential. The distance distributions above similar to 10 eV are compatible with nitrogen Rydberg states correlating to the doubly excited Rydberg state manifold below the ionic 2(4) Sigma(-) level.

  • 60.
    Zhaunerchyk, Vitali
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Rosen, Stefan
    Stockholm University, Faculty of Science, Department of Physics.
    Vigren, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Hamberg, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Kashperka, Iryna
    Stockholm University, Faculty of Science, Department of Physics.
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, Department of Physics.
    Semaniak, Jacek
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Investigation into the vibrational yield of OH products in the OH plus H plus H channel arising from the dissociative recombination of H3O+2009In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 130, no 21, p. 214302-Article in journal (Refereed)
    Abstract [en]

    The vibrational population of the hydroxyl radical, OH, formed in the OH+H+H channel arising from the dissociative recombination of the hydronium ion, H3O+, has been investigated at the storage ring CRYRING using a position-sensitive imaging detector. Analysis shows that the OH fragments are predominantly produced in the v=0 and v=1 states with almost equal probabilities. This observation is in disagreement with earlier FALP experiments, which reported OH(v=0) as the dominant product. Possible explanations for this difference are discussed.

  • 61.
    Zhaunerchyk, Vitali
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Hellberg, Fredrik
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Ehlerding, Anneli
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Vane, C. Randy
    Bannister, Mark E.
    Bahati, Eric M.
    Österdahl, Fabian
    af Ugglas, Magnus
    Stockholm University, Faculty of Science, The Manne Siegbahn Laboratory .
    Dissociative recombination study of PD2+ at CRYRING: absolute cross section, chemical branching ratios and three-body fragmentation dynamics2005In: Molecular Physics, ISSN 0026-8976, E-ISSN 1362-3028, Molecular Physics, ISSN 0026-8976, Vol. 103, no 20, p. 2735-2745Article in journal (Refereed)
    Abstract [en]

    The paper reports an investigation of the dissociative recombination of   at the heavy-ion storage ring CRYRING. The absolute cross-section has been measured as a function of centre-of-mass energy ranging from 1 meV to 0.1 eV. The experiment performed has shown the dissociative recombination of   to be dominated by three-body break-up, with a branching ratio of about 78%. Competition between the available three-body channels producing the ground state, P(4S), and the first two excited states, P(2D) and P(2P), is observed. The formation of the first excited state dominates over the other two almost equally probable channels with about 75% of all three-body events. The results indicate that the kinetic energy released in the three-body break-up of   is randomly shared between the deuterium atoms. The intra-molecular angle on dissociation has also been investigated. A comparative analysis of the dissociative recombination dynamics for the two isovalent systems,   and  , is undertaken.

  • 62.
    Zhaunerchyk, Vitali
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, Magdalena
    Stockholm University, Faculty of Science, Department of Physics.
    Vigren, Erik
    Stockholm University, Faculty of Science, Department of Physics.
    Hamberg, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, Mats
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, Richard D.
    Stockholm University, Faculty of Science, Department of Physics.
    Semaniak, Jacek
    Sequential formation of the CH3+H+H channel in the dissociative recombination of CH5+2009In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 79, no 3, p. 30701-Article in journal (Refereed)
    Abstract [en]

    The fragmentation dynamics in the CH3+H+H channel arising from the dissociative recombination of protonated methane, CH5+, has been investigated with an imaging detector at the CRYRING storage ring. The experimental results imply that this channel proceeds via two-step break-up in which the intermediate CH4 molecule is sufficiently internally excited to further fragment. These observations could go some way to explaining the discrepancy in results reported from ion storage rings and FALP apparatus.

  • 63.
    Zhaunerchyk, Vitali
    et al.
    Stockholm University, Faculty of Science, Department of Physics.
    Thomas, R. D.
    Stockholm University, Faculty of Science, Department of Physics.
    Geppert, Wolf D.
    Stockholm University, Faculty of Science, Department of Physics.
    Hamberg, Mathias
    Stockholm University, Faculty of Science, Department of Physics.
    Kaminska, M.
    Stockholm University, Faculty of Science, Department of Physics.
    Vigren, E.
    Stockholm University, Faculty of Science, Department of Physics.
    Larsson, M.
    Stockholm University, Faculty of Science, Department of Physics.
    Dissociative recombination of D2H+: Comparison between recent storage-ring results and theoretical calculations2008In: Physical Review A. Atomic, Molecular, and Optical Physics, ISSN 1050-2947, E-ISSN 1094-1622, Vol. 77, no 3, p. 34701-Article in journal (Refereed)
    Abstract [en]

    The most up-to-date theoretical calculation on the dissociative recombination (DR) of D2H+ predicts a 2-5 times lower rate coefficient than that obtained experimentally at the Test Storage Ring (TSR). In order to verify the validity either of the experimental results or the theoretical calculations we have studied the DR of D2H+ at the storage ring CRYRING. The rate coefficient has been measured over the interaction energy range from approximate to 0 eV to 50 eV and has been found to have a peak at about 10 eV with a value of 1.6 x 10(-8) cm(3) s(-1), which is in excellent agreement with the result reported from TSR. Taking into account the electron temperature distributions, excellent agreement between the two storage rings measurements is also obtained at smaller interaction energies. The branching fraction analysis has been performed at approximate to 0 eV interaction energy and revealed the following results at the 1 sigma confidence level: N(D+D+H)=76.5%+/-2.2%, N(D-2+H)= 10.0%+/-0.7%, and N(DH+D)=13.5%+/-1.5%. The value of 2N(D-2+H)/N(DH+D)=1.48+/-0.22 implies that formation of D-2 is more favorable than DH.

  • 64. Ziurys, L. M.
    et al.
    Halfen, D. T.
    Geppert, Wolf
    Stockholm University, Faculty of Science, Department of Physics.
    Aikawa, Y.
    Following the Interstellar History of Carbon: From the Interiors of Stars to the Surfaces of Planets2016In: Astrobiology, ISSN 1531-1074, E-ISSN 1557-8070, Vol. 16, no 12, p. 997-1012Article in journal (Refereed)
    Abstract [en]

    The chemical history of carbon is traced from its origin in stellar nucleosynthesis to its delivery to planet surfaces. The molecular carriers of this element are examined at each stage in the cycling of interstellar organic material and their eventual incorporation into solar system bodies. The connection between the various interstellar carbon reservoirs is also examined. Carbon has two stellar sources: supernova explosions and mass loss from evolved stars. In the latter case, the carbon is dredged up from the interior and then ejected into a circumstellar envelope, where a rich and unusual C-based chemistry occurs. This molecular material is eventually released into the general interstellar medium through planetary nebulae. It is first incorporated into diffuse clouds, where carbon is found in polyatomic molecules such as H2CO, HCN, HNC, c-C3H2, and even C-60(+). These objects then collapse into dense clouds, the sites of star and planet formation. Such clouds foster an active organic chemistry, producing compounds with a wide range of functional groups with both gas-phase and surface mechanisms. As stars and planets form, the chemical composition is altered by increasing stellar radiation, as well as possibly by reactions in the presolar nebula. Some molecular, carbon-rich material remains pristine, however, encapsulated in comets, meteorites, and interplanetary dust particles, and is delivered to planet surfaces.

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