Production of H + 3 via photodissociation of organic molecules in interstellar clouds

We present experimental results obtained from photoionization and photodissociation processes of abundant interstellar CH 3 ‐X type organic molecules like methanol (CH 3 OH), methylamine (CH 3 NH 2 ) and acetonitrile (CH 3 CN) as alternative route for the production of H + 3 in interstellar and star‐forming environments. The measurements were taken at the Brazilian Synchrotron Light Laboratory (LNLS), employing soft X‐ray photons with energies between 200 and 310 eV and time‐of‐flight (TOF) mass spectrometry. Mass spectra were obtained using the photoelectron–photoion coincidence techniques. Absolute averaged cross‐sections for H + 3 production by soft X‐rays were determined. We have found that, among the channels leading to molecular dissociation, the H + 3 yield could reach values up to 0.7 per cent for single photoionization process and up to 4 per cent for process involving double photoionization. The H + 3 photoproduction cross‐section due to the dissociation of the studied organic molecules by photons over the C1s edge (200–310 eV) were about 0.2–1.4 × 10 −18 cm 2 . Adopting the typical X‐ray luminosity L X ≳ 10 31 erg s −1 which best fit the observational data for AFGL 2591 we derive an estimative for the H + 3 photoproduction rate due to methyl compound dissociation process. The highest value for the H + 3 column density from methanol dissociation by soft X‐rays, assuming a steady state scenario, was about 10 11 cm 2 , which gives the fraction of the photoproduced H + 3 of about 0.05 per cent, as in the case of dense molecular cloud AFGL 2591. Despite the extreme small value, this represent a new and alternative source of H + 3 into dense molecular clouds and it is not been considered as yet in interstellar chemistry models.