2007MNRAS.375.1488P

We present experimental results obtained from photoionization and photodissociation processes of abundant interstellar CH₃-X type organic molecules like methanol (CH₃OH), methylamine (CH₃NH₂) and acetonitrile (CH₃CN) as alternative route for the production of H⁺₃in 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⁺₃production by soft X-rays were determined. We have found that, among the channels leading to molecular dissociation, the H⁺₃yield 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⁺₃photoproduction cross-section due to the dissociation of the studied organic molecules by photons over the C1s edge (200-310 eV) were about 0.2-1.4x10^–18 cm². Adopting the typical X-ray luminosity L_X≳ 10³¹ erg/s which best fit the observational data for AFGL 2591 we derive an estimative for the H⁺₃photoproduction rate due to methyl compound dissociation process. The highest value for the H⁺₃column density from methanol dissociation by soft X-rays, assuming a steady state scenario, was about 10¹¹ cm², which gives the fraction of the photoproduced H⁺₃of 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⁺₃into dense molecular clouds and it is not been considered as yet in interstellar chemistry models.