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Nixon CA. The Composition and Chemistry of Titan's Atmosphere. ACS EARTH & SPACE CHEMISTRY 2024; 8:406-456. [PMID: 38533193 PMCID: PMC10961852 DOI: 10.1021/acsearthspacechem.2c00041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Revised: 11/02/2023] [Accepted: 02/02/2024] [Indexed: 03/28/2024]
Abstract
In this review I summarize the current state of knowledge about the composition of Titan's atmosphere and our current understanding of the suggested chemistry that leads to that observed composition. I begin with our present knowledge of the atmospheric composition, garnered from a variety of measurements including Cassini-Huygens, the Atacama Large Millimeter/submillimeter Array, and other ground- and space-based telescopes. This review focuses on the typical vertical profiles of gases at low latitudes rather than global and temporal variations. The main body of the review presents a chemical description of how complex molecules are believed to arise from simpler species, considering all known "stable" molecules-those that have been uniquely identified in the neutral atmosphere. The last section of the review is devoted to the gaps in our present knowledge of Titan's chemical composition and how further work may fill those gaps.
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Affiliation(s)
- Conor A. Nixon
- Planetary Systems Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, Maryland 20771, United
States
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Crisci L, Di Grande S, Cavallotti C, Barone V. Toward an Accurate Black-Box Tool for the Kinetics of Gas-Phase Reactions Involving Barrier-less Elementary Steps. J Chem Theory Comput 2023; 19:7626-7639. [PMID: 37880932 PMCID: PMC10653117 DOI: 10.1021/acs.jctc.3c00857] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2023] [Revised: 10/06/2023] [Accepted: 10/13/2023] [Indexed: 10/27/2023]
Abstract
An enhanced computational protocol has been devised for the accurate characterization of gas-phase barrier-less reactions in the framework of the reaction-path (RP) and variable reaction coordinate variational transition-state theory. In particular, the synergistic combination of density functional theory and Monte Carlo sampling to optimize reactive fluxes led to a reliable yet effective computational workflow. A black-box strategy has been developed for selecting the most suited density functional with reference to a high-level one-dimensional reference potential. At the same time, different descriptions of hindered rotations are automatically selected, depending on the corresponding harmonic frequencies along the RP. The performance of the new tool is investigated by means of two prototypical reactions involving different degrees of static and dynamic correlation, namely, H2S + Cl and CH3 + CH3. The remarkable agreement of the computed kinetic parameters with the available experimental data confirms the accuracy and robustness of the proposed approach. Together with their intrinsic interest, these results also pave the way toward systematic investigations of gas-phase reactions involving barrier-less elementary steps by a reliable, user-friendly tool, which can be confidently used also by nonspecialists.
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Affiliation(s)
- Luigi Crisci
- Scuola
Normale Superiore di Pisa, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
- Department
of Chemical Sciences, University of Napoli
Federico II, Complesso Universitario di M.S. Angelo, via Cintia 21, I-80126 Napoli, Italy
| | - Silvia Di Grande
- Scuola
Normale Superiore di Pisa, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
- Scuola
Superiore Meridionale, Largo San Marcellino 10, I-80138 Napoli, Italy
| | - Carlo Cavallotti
- Department
of Chemistry, Materials and Chemical Engineering “G. Natta”, Politecnico di Milano, I-20131 Milano, Italy
| | - Vincenzo Barone
- Scuola
Normale Superiore di Pisa, Piazza dei Cavalieri 7, I-56126 Pisa, Italy
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Yao Q, Cao XM, Zong WG, Sun XH, Li ZR, Li XY. Potential Energy Surface for Large Barrierless Reaction Systems: Application to the Kinetic Calculations of the Dissociation of Alkanes and the Reverse Recombination Reactions. J Phys Chem A 2018; 122:4869-4881. [PMID: 29757648 DOI: 10.1021/acs.jpca.8b00877] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The isodesmic reaction method is applied to calculate the potential energy surface (PES) along the reaction coordinates and the rate constants of the barrierless reactions for unimolecular dissociation reactions of alkanes to form two alkyl radicals and their reverse recombination reactions. The reaction class is divided into 10 subclasses depending upon the type of carbon atoms in the reaction centers. A correction scheme based on isodesmic reaction theory is proposed to correct the PESs at UB3LYP/6-31+G(d,p) level. To validate the accuracy of this scheme, a comparison of the PESs at B3LYP level and the corrected PESs with the PESs at CASPT2/aug-cc-pVTZ level is performed for 13 representative reactions, and it is found that the deviations of the PESs at B3LYP level are up to 35.18 kcal/mol and are reduced to within 2 kcal/mol after correction, indicating that the PESs for barrierless reactions in a subclass can be calculated meaningfully accurately at a low level of ab initio method using our correction scheme. High-pressure limit rate constants and pressure dependent rate constants of these reactions are calculated based on their corrected PESs and the results show the pressure dependence of the rate constants cannot be ignored, especially at high temperatures. Furthermore, the impact of molecular size on the pressure-dependent rate constants of decomposition reactions of alkanes and their reverse reactions has been studied. The present work provides an effective method to generate meaningfully accurate PESs for large molecular system.
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Blitz MA, Seakins PW. Laboratory studies of photochemistry and gas phase radical reaction kinetics relevant to planetary atmospheres. Chem Soc Rev 2012; 41:6318-47. [DOI: 10.1039/c2cs35204d] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Kaiser RI, Maksyutenko P, Ennis C, Zhang F, Gu X, Krishtal SP, Mebel AM, Kostko O, Ahmed M. Untangling the chemical evolution of Titan's atmosphere and surface–from homogeneous to heterogeneous chemistry. Faraday Discuss 2010; 147:429-78; discussion 527-52. [DOI: 10.1039/c003599h] [Citation(s) in RCA: 109] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Huang CH, Kaiser RI, Chang AHH. Theoretical Study on the Reaction of Ground State Cyano Radical with Propylene in Titan’s Atmosphere. J Phys Chem A 2009; 113:12675-85. [DOI: 10.1021/jp905081u] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- C. H. Huang
- Department of Chemistry, National Dong Hwa University, Shoufeng, Hualien 974, Taiwan, and Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii 96822
| | - R. I. Kaiser
- Department of Chemistry, National Dong Hwa University, Shoufeng, Hualien 974, Taiwan, and Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii 96822
| | - A. H. H. Chang
- Department of Chemistry, National Dong Hwa University, Shoufeng, Hualien 974, Taiwan, and Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii 96822
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Gu X, Zhang F, Kaiser RI. Reaction dynamics on the formation of 1- and 3-cyanopropylene in the crossed beams reaction of ground-state cyano radicals (CN) with propylene (C3H6) and its deuterated isotopologues. J Phys Chem A 2008; 112:9607-13. [PMID: 18681396 DOI: 10.1021/jp8039059] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Crossed molecular beams experiments were utilized to explore the chemical reaction dynamics of ground-state cyano radicals, CN(X(2)Sigma(+)), with propylene (CH3CHCH2) together with two d3-isotopologues (CD3CHCH2, CH3CDCD2) as potential pathways to form organic nitriles under single collision conditions in the atmosphere of Saturn's moon Titan and in the interstellar medium. On the basis of the center-of-mass translational and angular distributions, the reaction dynamics were deduced to be indirect and commenced via an addition of the electrophilic cyano radical with its radical center to the alpha-carbon atom of the propylene molecule yielding a doublet radical intermediate: CH3CHCH2CN. Crossed beam experiments with propylene-1,1,2-d3 (CH3CDCD2) and propylene-3,3,3-d3 (CD3CHCH2) indicated that the reaction intermediates CH3CDCD2CN (from propylene-1,1,2-d3) and CD3CHCH2CN (from propylene-3,3,3-d3) eject both atomic hydrogen through tight exit transition states located about 40-50 kJ mol(-1) above the separated products: 3-butenenitrile [H2CCDCD2CN] (25%), and cis/trans-2-butenenitrile [CD3CHCHCN] (75%), respectively, plus atomic hydrogen. Applications of our results to the chemical processing of cold molecular clouds like TMC-1 and OMC-1 are also presented.
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Affiliation(s)
- Xibin Gu
- Department of Chemistry, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA
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Landera A, Krishtal SP, Kislov VV, Mebel AM, Kaiser RI. Theoretical study of the C6H3 potential energy surface and rate constants and product branching ratios of the C2H(Σ+2)+C4H2(Σg+1) and C4H(Σ+2)+C2H2(Σg+1) reactions. J Chem Phys 2008; 128:214301. [DOI: 10.1063/1.2929821] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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Li H, Chen BZ, Huang MB. CASPT2 investigation of ethane dissociation and methyl recombination using canonical variational transition state theory. INT J CHEM KINET 2008. [DOI: 10.1002/kin.20299] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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Parker JK, Payne WA, Cody RJ, Nesbitt FL, Stief LJ, Klippenstein SJ, Harding LB. Direct Measurement and Theoretical Calculation of the Rate Coefficient for Cl + CH3 in the Range from T = 202−298 K. J Phys Chem A 2007; 111:1015-23. [PMID: 17253663 DOI: 10.1021/jp066231v] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The rate coefficient has been measured under pseudo-first-order conditions for the Cl+CH3 association reaction at T=202, 250, and 298 K and P=0.3-2.0 Torr helium using the technique of discharge-flow mass spectrometry with low-energy (12-eV) electron-impact ionization and collision-free sampling. Cl and CH3 were generated rapidly and simultaneously by reaction of F with HCl and CH4, respectively. Fluorine atoms were produced by microwave discharge in an approximately 1% mixture of F2 in He. The decay of CH3 was monitored under pseudo-first-order conditions with the Cl-atom concentration in large excess over the CH3 concentration ([Cl]0/[CH3]0=9-67). Small corrections were made for both axial and radial diffusion and minor secondary chemistry. The rate coefficient was found to be in the falloff regime over the range of pressures studied. For example, at T=202 K, the rate coefficient increases from 8.4x10(-12) at P=0.30 Torr He to 1.8x10(-11) at P=2.00 Torr He, both in units of cm3 molecule-1 s-1. A combination of ab initio quantum chemistry, variational transition-state theory, and master-equation simulations was employed in developing a theoretical model for the temperature and pressure dependence of the rate coefficient. Reasonable empirical representations of energy transfer and of the effect of spin-orbit interactions yield a temperature- and pressure-dependent rate coefficient that is in excellent agreement with the present experimental results. The high-pressure limiting rate coefficient from the RRKM calculations is k2=6.0x10(-11) cm3 molecule-1 s-1, independent of temperature in the range from 200 to 300 K.
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Affiliation(s)
- James K Parker
- Solar System Exploration Division, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
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Hébrard E, Dobrijevic M, Bénilan Y, Raulin F. Photochemical kinetics uncertainties in modeling Titan’s atmosphere: A review. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY C-PHOTOCHEMISTRY REVIEWS 2006. [DOI: 10.1016/j.jphotochemrev.2006.12.004] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Klippenstein SJ, Georgievskii Y, Harding LB. Predictive theory for the combination kinetics of two alkyl radicals. Phys Chem Chem Phys 2006; 8:1133-47. [PMID: 16633594 DOI: 10.1039/b515914h] [Citation(s) in RCA: 129] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
An ab initio transition state theory based procedure for accurately predicting the combination kinetics of two alkyl radicals is described. This procedure employs direct evaluations of the orientation dependent interaction energies at the CASPT2/cc-pvdz level within variable reaction coordinate transition state theory (VRC-TST). One-dimensional corrections to these energies are obtained from CAS+1+2/aug-cc-pvtz calculations for CH3 + CH3 along its combination reaction path. Direct CAS+1+2/aug-cc-pvtz calculations demonstrate that, at least for the purpose of predicting the kinetics, the corrected CASPT2/cc-pvdz potential energy surface is an accurate approximation to the CAS+1+2/aug-cc-pvtz surface. Furthermore, direct trajectory simulations, performed at the B3LYP/6-31G* level, indicate that there is little local recrossing of the optimal VRC transition state dividing surface. The corrected CASPT2/cc-pvdz potential is employed in obtaining direct VRC-TST kinetic predictions for the self and cross combinations of methyl, ethyl, iso-propyl, and tert-butyl radicals. Comparisons with experiment suggest that the present dynamically corrected VRC-TST approach provides quantitatively accurate predictions for the capture rate. Each additional methyl substituent adjacent to a radical site is found to reduce the rate coefficient by about a factor of two. In each instance, the rate coefficients are predicted to decrease quite substantially with increasing temperature, with the more sterically hindered reactants having a more rapid decrease. The simple geometric mean rule, relating the capture rate for the cross reaction to those for the self-reactions, is in remarkably good agreement with the more detailed predictions. With suitable generalizations the present approach should be applicable to a wide array of radical-radical combination reactions.
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Affiliation(s)
- Stephen J Klippenstein
- Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551-0969, USA.
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Moses JI, Fouchet T, Bézard B, Gladstone GR, Lellouch E, Feuchtgruber H. Photochemistry and diffusion in Jupiter's stratosphere: Constraints from ISO observations and comparisons with other giant planets. ACTA ACUST UNITED AC 2005. [DOI: 10.1029/2005je002411] [Citation(s) in RCA: 141] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- J. I. Moses
- Lunar and Planetary Institute; Houston Texas USA
| | - T. Fouchet
- LESIA; Observatoire de Paris; Meudon France
- Université Paris 6; Paris France
| | - B. Bézard
- LESIA; Observatoire de Paris; Meudon France
| | - G. R. Gladstone
- Space Sciences Department; Southwest Research Institute; San Antonio Texas USA
| | | | - H. Feuchtgruber
- Max-Planck-Institut für Extraterrestrische Physik; Garching Germany
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Pimentel AS, Payne WA, Nesbitt FL, Cody RJ, Stief LJ. Rate Constant for the Reaction H + C2H5 at T = 150−295 K. J Phys Chem A 2004. [DOI: 10.1021/jp040204s] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- André S. Pimentel
- Laboratory for Extraterrestrial Physics, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, and Department of Chemistry, Catholic University of America, Washington, DC 20064
| | - Walter A. Payne
- Laboratory for Extraterrestrial Physics, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, and Department of Chemistry, Catholic University of America, Washington, DC 20064
| | - Fred L. Nesbitt
- Laboratory for Extraterrestrial Physics, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, and Department of Chemistry, Catholic University of America, Washington, DC 20064
| | - Regina J. Cody
- Laboratory for Extraterrestrial Physics, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, and Department of Chemistry, Catholic University of America, Washington, DC 20064
| | - Louis J. Stief
- Laboratory for Extraterrestrial Physics, NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771, and Department of Chemistry, Catholic University of America, Washington, DC 20064
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15
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Wilson EH. Current state of modeling the photochemistry of Titan's mutually dependent atmosphere and ionosphere. ACTA ACUST UNITED AC 2004. [DOI: 10.1029/2003je002181] [Citation(s) in RCA: 285] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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