skip to main content

SciTech ConnectSciTech Connect

Title: Low temperature rate coefficients of the H + CH{sup +} → C{sup +} + H{sub 2} reaction: New potential energy surface and time-independent quantum scattering

The observed abundances of the methylidyne cation, CH{sup +}, in diffuse molecular clouds can be two orders of magnitude higher than the prediction of the standard gas-phase models which, in turn, predict rather well the abundances of neutral CH. It is therefore necessary to investigate all the possible formation and destruction processes of CH{sup +} in the interstellar medium with the most abundant species H, H{sub 2}, and e{sup −}. In this work, we address the destruction process of CH{sup +} by hydrogen abstraction. We report a new calculation of the low temperature rate coefficients for the abstraction reaction, using accurate time-independent quantum scattering and a new high-level ab initio global potential energy surface including a realistic model of the long-range interaction between the reactants H and CH{sup +}. The calculated thermal rate coefficient is in good agreement with the experimental data in the range 50 K–800 K. However, at lower temperatures, the experimental rate coefficient takes exceedingly small values which are not reproduced by the calculated rate coefficient. Instead, the latter rate coefficient is close to the one given by the Langevin capture model, as expected for a reaction involving an ion and a neutral species. Several recent theoreticalmore » works have reported a seemingly good agreement with the experiment below 50 K, but an analysis of these works show that they are based on potential energy surfaces with incorrect long-range behavior. The experimental results were explained by a loss of reactivity of the lowest rotational states of the reactant; however, the quantum scattering calculations show the opposite, namely, a reactivity enhancement with rotational excitation.« less
Authors:
 [1] ;  [2] ; ;  [1] ;  [3] ;  [4] ;  [5] ;  [2]
  1. Université de Bordeaux, Institut des Sciences Moléculaires, CNRS UMR 5255, 33405 Talence Cedex (France)
  2. (Tunisia)
  3. Université de Bourgogne Franche-Comté, Laboratoire Interdisciplinaire Carnot de Bourgogne, CNRS UMR 6303, 21078 Dijon Cedex (France)
  4. (France)
  5. Faculté des Sciences de Tunis, Université de Tunis El-Manar, Laboratoire de Physique de la Matière Condensée, 2092 Tunis (Tunisia)
Publication Date:
OSTI Identifier:
22489603
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 143; Journal Issue: 11; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; CARBON IONS; CATIONS; EXCITATION; EXPERIMENTAL DATA; HYDROGEN; INTERACTION RANGE; POTENTIAL ENERGY; REACTIVITY; ROTATIONAL STATES; SCATTERING; SURFACES