Breakdown curves of CH₂⁽⁺⁾, CH₃⁽⁺⁾, and CH₄⁽⁺⁾ molecules

I. Construction and application to electron collisions and UV photodissociation

¹ Institut de Physique Nucléaire d’Orsay (IPNO), CNRS, Université Paris Sud, Université Paris-Saclay, 91406 Orsay, France
e-mail: chabot@ipno.in2p3.fr
² Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Université Paris Sud, Université Paris-Saclay, 91405 Orsay, France
³ Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse cedex 4, France
⁴ Departamento de Química, Módulo 13, Condensed Matter Physic Center (IFIMAC), Institute for advanced Research in Chemical Sciences (IAdChem), Universidad Autónoma de Madrid, 28049 Madrid, Spain

Received: 24 April 2019
Accepted: 9 June 2019

Abstract

Aims. The aim of this work is to furnish branching ratios (BRs) to the kinetic databases used in astrochemistry such as the KInetic Database for Astrochemistry (KIDA). This concerns CH_y⁽⁺⁾ species (y = 2–4) excited by cosmic rays, electrons and photons, or the intermediate excited complexes CH_y⁽⁺⁾ resulting from a chemical reaction.

Methods. The full set of fragmentation branching ratios following CH_y⁽⁺⁾ (y = 2,4) of constant velocity (250 keV uma⁻¹) colliding with He atoms has been measured with the multidetector AGAT. Kinetic energy distributions of neutral fragments produced in each dissociation channel have been also measured. With these experimental inputs, and theoretical dissociation energies, semiempirical breakdown curves (BDCs) have been constructed.

Results. Prediction of BRs with the present BDCs is found to agree with available BR measurements for electronic dissociative recombination, collision with fast electron and photodissociation. Dependence of BRs with the various UV fields relevant to interstellar medium and planetary atmospheres is predicted.