scholarly journals Collisional excitation of complex organic molecules

2008 ◽  
Vol 4 (S251) ◽  
pp. 137-138 ◽  
Author(s):  
Alexandre Faure ◽  
Eric Josselin ◽  
Laurent Wiesenfeld ◽  
Cecilia Ceccarelli
Keyword(s):  
Gas Phase ◽  
Degrees Of Freedom ◽  
Organic Molecules ◽  
Low Frequency ◽  
Rate Coefficients ◽  
Collisional Excitation ◽  
Phase Complex ◽  
Collisional Rate Coefficients ◽  
Complex Organic ◽  
Collisional Rate

AbstractA major difficulty in modelling the infrared and (sub)millimeter spectra of gas-phase complex organic molecules is the lack of state-to-state collisional rate coefficients. Accurate quantum or classical scattering calculations for large polyatomic species are indeed computationally highly challenging, particularly when both rotation and low frequency vibrations such as bending and torsional modes are involved. We briefly present here an approximate approach to estimate and/or extrapolate rotational and rovibrational rates for polyatomic molecules with many degrees of freedom.

Collisional excitation of H2S by molecular hydrogen

2020 ◽  
Vol 494 (4) ◽  
pp. 5239-5243
Author(s):  
Paul J Dagdigian
Keyword(s):  
Energy Surface ◽  
Rate Coefficients ◽  
Cluster Method ◽  
Quantum Scattering ◽  
Collisional Excitation ◽  
Close Coupling ◽  
Accurate Knowledge ◽  
Explicitly Correlated ◽  
Collisional Rate Coefficients ◽  
Collisional Rate

ABSTRACT Accurate estimates of the abundance of H2S, and inferences about the unmeasured H2 density, require accurate knowledge of radiative and collisional rate coefficients. Time-independent close-coupling quantum scattering calculations have been employed to compute rate coefficients for (de-)excitation of para- and ortho-H2S in collisions with para- and ortho-H2. These calculations utilized a potential energy surface for the interaction of H2S with H2 recently computed by the explicitly correlated CCSD(T)-F12a coupled-cluster method. Rate coefficients for temperatures ranging from 5 to 500 K were calculated for all transitions among the first 19 rotational levels of H2S, whose energies are less than or equal to 405 K. These rate coefficients are compared with previous estimates of these quantities.

Collisional excitation of methylene by molecular hydrogen

2021 ◽  
Vol 508 (1) ◽  
pp. 118-124
Author(s):  
Paul J Dagdigian
Keyword(s):  
Energy Surface ◽  
Energy Levels ◽  
Rate Coefficients ◽  
Coupled Cluster ◽  
Collisional Excitation ◽  
Work Time ◽  
Close Coupling ◽  
Collisional Rate Coefficients ◽  
Collisional Rate ◽  
Cluster Level

ABSTRACT Accurate estimates of the abundance of methylene (CH2) in the interstellar medium require knowledge of both the radiative and collisional rate coefficients for the transfer of population between rotational levels. In this work, time-independent quantum close coupling calculations have been carried out to compute rate coefficients for the (de-)excitation of ortho- and para-CH2 in collisions with ortho- and para-H2. These scattering calculations have employed a recently computed, high-quality potential energy surface, based on the coupled cluster level of theory [RCCSD(T)-F12a], for the interaction of CH2 in its ground $\tilde{X} ^3B_1$ electronic state with H2. The collisional rate coefficients were obtained for all fine-structure transitions among the first 22 and 24 energy levels of ortho- and para-CH2, respectively, having energies less than 277 cm−1. These rate coefficients are compared with previous calculated values, obtained by scaling data for CH2–He. In the case of ortho-CH2, whose levels display hyperfine structure, rate coefficients for transitions between hyperfine levels were also computed, by the MJ randomization approximation. Finally, some simple radiative transfer calculations are presented.

Gas-phase reactivity of CH3OH+OH down to 11.7 K: Astrophysical implications

2019 ◽  
Vol 15 (S350) ◽  
pp. 365-367
Author(s):  
Antonio J. Ocaña ◽  
Sergio Blázquez ◽  
Daniel González ◽  
Alexey Potapov ◽  
Bernabé Ballesteros ◽  
...  
Keyword(s):  
Gas Phase ◽  
Molecular Clouds ◽  
Organic Molecules ◽  
Rate Coefficients ◽  
Reaction Networks ◽  
Oh Radicals ◽  
Temperature Reaction ◽  
Starting Point ◽  
Prebiotic Molecules ◽  
Complex Organic

AbstractMethanol (CH3OH) and hydroxyl (OH) radicals are two species abundant in cold and dense molecular clouds which are important for the chemistry of the interstellar medium (ISM). CH3OH is a well-known starting point for the formation of more complex organic molecules (COMs) in these molecular clouds. Thus, the reactivity of CH3OH in the gas-phase with OH may play a crucial role in the formation of species as complex as prebiotic molecules in the ISM and reliable rate coefficients should be used in astrochemical models describing low temperature reaction networks.

Calculations of fine-structure resolved collisional rate coefficients for the NH(X3Σ−)-He system

2011 ◽  
Vol 134 (2) ◽  
pp. 024305 ◽  
Author(s):  
Robert Toboła ◽  
Fabien Dumouchel ◽  
Jacek Kłos ◽  
François Lique
Keyword(s):  
Fine Structure ◽  
Rate Coefficients ◽  
Collisional Rate Coefficients ◽  
Collisional Rate

Collisional-Rate Coefficients for Sodiumlike Ar viii Ions

1972 ◽  
Vol 6 (1) ◽  
pp. 38-44 ◽  
Author(s):  
R. U. Datla ◽  
H. -J. Kunze ◽  
D. Petrini
Keyword(s):  
Rate Coefficients ◽  
Collisional Rate Coefficients ◽  
Collisional Rate

Chemical mechanism for the decomposition of CH3NH2 and implications to interstellar glycine

2020 ◽  
Vol 501 (1) ◽  
pp. 1202-1214
Author(s):  
Diego N de Jesus ◽  
Jean M B A da Silva ◽  
Tatiane N Tejero ◽  
Gladson de Souza Machado ◽  
Neubi F Xavier ◽  
...  
Keyword(s):  
Spectroscopic Data ◽  
Transition State Theory ◽  
Organic Molecules ◽  
State Theory ◽  
Chemical Mechanism ◽  
Rate Coefficients ◽  
Interstellar Ice ◽  
Chemical Behaviour ◽  
Tunnelling Effects ◽  
Complex Organic

ABSTRACT Complex organic molecules from extraterrestrial source are expected to have contributed to the Early Earth chemistry. Methylamine (CH3NH2)has already been observed in the interstellar medium (ISM) and is generally related to the formation of glycine, although the latter has not been identified in the ISM yet. In this work, a chemical model for CH3NH2 was investigated, comprising twenty-eight reactions and including reactions involving NH3 and HOOC, aiming to understand the main routes for formation and decomposition of methylamine and also to infer about the chemical behaviour of glycine in the ISM. Calculations were performed at the CCSD(T)/aug-cc-pVTZ//M06-2X/aug-cc-pVTZ level and rate coefficients were calculated adopting the canonical variational transition state theory (CVTST), in the temperature range 100 to 4000 K, including tunnelling effects. Starting from HCN, the preferred pathway for methylamine formation is through consecutive hydrogenation steps, forming CH2N, CH2NH, and CH2NH2 intermediates. Considering the decomposition, dissociation into CH3 and NH2 is the most favourable step. NH3 and HCN are common compounds in interstellar ice analogues and react producing NH2 and CH2N through NH2NCH2 and H2NCH2N intermediates. The latter is proposed here and spectroscopic data for any future experimental investigation are given. Finally, an extension to the ISM glycine chemistry is explored and routes to its formation, from the simplest compounds found in interstellar ices, are proposed.

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