High accuracy thermochemistry and kinetics of the HCN/HNC system

Lee, Kelvin

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https://hdl.handle.net/2142/100522 Copy

Description

Title

High accuracy thermochemistry and kinetics of the HCN/HNC system

Author(s)

Lee, Kelvin

Contributor(s)

McCarthy, Michael C.

Issue Date

2018-06-20

Keyword(s)

Astronomy

Abstract

The relative abundance of HCN/HNC is a ubiquitous issue in astrochemistry. This ratio is largely governed by competition between thermodynamic stability and kinetics: in cold dense clouds, the thermodynamically unfavorable HNC is enhanced, while in hot cores and young stellar objects there is a much stronger preference for HCN. Efforts to develop a consistent and universally accepted set of reaction rates and thermochemical parameters involving both gas- and condensed-phase dynamics has proven challenging. Considerable interest has focused on accurate determinations of molecular properties, and many theoretical and experimental efforts, spanning several decades, have sought to provide the necessary rates and enthalpies. Despite much work, estimates of the uncertainty of enthalpies and rates vary substantially, particularly with respect to quantum chemical treatments that involve a plethora of basis sets and methods. To address this issue, we have undertaken a systematic study to calculate a consistent set of thermochemical quantities and rates involving gas-phase reactions presumed to be important in determining the branching between HCN and HNC in astrophysical environments. Using the HEAT345(Q) method, we have calculated the energetics of neutral and ion reactants and products. This method routinely achieves chemical accuracy (~1 kJ/mol/120 K) without empirical corrections. We validate our thermochemical network by comparison with reliable databases such as the ATcT, and by doing so lends confidence into the species that are not yet included in databases. Finally, we report reaction rates for significant reactions from first principles (V)TST theory.

Publisher

International Symposium on Molecular Spectroscopy

Type of Resource

text

Language

eng

Permalink

http://hdl.handle.net/2142/100522

DOI

10.15278/isms.2018.WL10

Copyright and License Information

Copyright 2018 Kelvin Lee

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