Rotational relaxation of HCO+ and DCO+ by collision with H2

Author:

Denis-Alpizar Otoniel1ORCID,Stoecklin Thierry2,Dutrey Anne3,Guilloteau Stéphane3

Affiliation:

1. Núcleo de Astroquímica y Astrofísica, Instituto de Ciencias Químicas Aplicadas, Facultad de Ingeniería, Universidad Autónoma de Chile, Av. Pedro de Valdivia 425, 7500912 Providencia, Santiago, Chile

2. Institut des Sciences Moléculaires, Université de Bordeaux, CNRS UMR 5255, F-33405 Talence Cedex, France

3. Laboratoire d’Astrophysique de Bordeaux, Université de Bordeaux, CNRS, B18N, Allée Geoffroy Saint-Hilaire, F-33615 Pessac, France

Abstract

ABSTRACT The HCO+ and DCO+ molecules are commonly used as tracers in the interstellar medium. Therefore, accurate rotational rate coefficients of these systems with He and H2 are crucial in non-local thermal equilibrium models. We determine in this work the rotational de-excitation rate coefficients of HCO+ in collision with both para- and ortho-H2, and also analyse the isotopic effects by studying the case of DCO+. A new four-dimensional potential energy surface from ab initio calculations was developed for the HCO+–H2 system, and adapted to the DCO+–H2 case. These surfaces are then employed in close-coupling calculations to determine the rotational de-excitation cross-sections and rate coefficients for the lower rotational states of HCO+ and DCO+. The new rate coefficients for HCO+ + para-H2 were compared with the available data, and a set of rate coefficients for HCO+ + ortho-H2 is also reported. The difference between the collision rates with ortho- and para-H2 is found to be small. These calculations confirm that the use of the rate coefficients for HCO+ + para-H2 for estimating those for HCO+ + ortho-H2 as well as for DCO+ + para-H2 is a good approximation.

Funder

Comisión Nacional de Investigación Científica y Tecnológica

Publisher

Oxford University Press (OUP)

Subject

Space and Planetary Science,Astronomy and Astrophysics

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