Breakdown curves of CH2(+),CH3(+) and CH4(+) molecules. I. Construction and application to electron collisions and UV photo-dissociation

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 species (y = 2–4) excited by cosmic rays, electrons and photons, or the intermediate excited complexes CH resulting from a chemical reaction.Methods. The full set of fragmentation branching ratios following CH (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.