2006/12/14 by S. Pilling, D. P. P. Andrade, R. Neves +3
Physics and Astronomy · #astro-ph
paper · pdf · doi:10.1111/j.1365-2966.2006.11415.x
published as Mon.Not.Roy.Astron.Soc.375:1488-1494,2007 · The paper contains 7 pages, 3 figures and 3 tables. Accepted to be published on MNRAS on 2006 December 14. Received 2006 December 14; in original form 2006 September 19
arxiv created 2006/12/14 · arxiv updated 2009/12/01
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 H3+ 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 mass spectrometry. Mass spectra were obtained using the photoelectron-photoion coincidence techniques. Absolute averaged cross sections for H3+ production by soft X-rays were determined. We have found that, among the channels leading to molecular dissociation, the H3+ yield could reach values up to 0.7% for single photoionization process and up to 4% for process involving double photoionization. The H3+ 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 cm2. Adopting the typical X-ray luminosity LX \gtrsim 1031 erg s-1 which best fit the observational data for AFGL 2591 (Stauber et al. 2005) we derive an estimative for the H3+ photoproduction rate due to methyl-compounds dissociation process. The highest value for the H3+ column density from methanol dissociation by soft X-rays, assuming a steady state scenario, was about 1011 cm2, which gives the fraction of the photoproduced H3+ of about 0.05%, as in the case of dense molecular cloud AFGL 2591. Despite the extreme small value, this represent a new and alternative source of H3+ into dense molecular clouds and it is not been considered as yet in interstellar chemistry models.