### Rotational relaxation of HCO+ and DCO+ by collision with H-2

### 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 H-2 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-H-2, 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+-H-2 system, and adapted to the DCO+-H-2 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-H-2 were compared with the available data, and a set of rate coefficients for HCO+ + ortho-H-2 is also reported. The difference between the collision rates with ortho- and para-H-2 is found to be small. These calculations confirm that the use of the rate coefficients for HCO+ + para-H-2 for estimating those for HCO+ + ortho-H-2 as well as for DCO+ + para-H-2 is a good approximation.

### Más información

Título según WOS: | Rotational relaxation of HCO+ and DCO+ by collision with H-2 |

Título de la Revista: | MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY |

Volumen: | 497 |

Número: | 4 |

Editorial: | OXFORD UNIV PRESS |

Fecha de publicación: | 2020 |

Página de inicio: | 4276 |

Página final: | 4281 |

DOI: |
10.1093/MNRAS/STAA2308 |

Notas: | ISI |