Experimental and theoretical studies on possible formation routes of organosulfur compounds in extraterrestrial environments

The reactions of atomic sulfur in the first excited metastable 1D state with C2H2, C2H4, and CH4 have been investigated at the most detailed level by means of the crossed molecular beam technique with mass spectrometric detection and ab initio calculations of the relevant potential energy surfaces. The nature of the primary products and their yield have been established and complemented with statistical estimates of product branching ratios. In the case of the reactions between S(1D) and C2H2/C2H4, we have observed the formation of molecular species containing a novel C��S bond, namely HCS, HCCS, CH2CS and CH2CHS. Therefore, these reactions are feasible routes of formation of organosulfur compounds in extraterrestrial environments where both S(1D) molecular precursors and simple hydrocarbons are present. In the S(1D)+C2H4 reaction the channel leading to HS+C2H3 is also important, while the HS+CH3 formation channel is the only one open for the reaction with methane. The two reactions are therefore a source of HS and hydrocarbon radicals. The observed reaction schemes can be generalized and extended to other reactions involving larger alkynes, alkenes and alkanes. Finally, the ionization energy of the HCCS radical has been determined to be 8.90.3 eV. The present results can help to unravel the complex impact-induced chemistry that occurred during the collision of Shoemaker-Levy 9 with Jupiter, to account for the inventory of sulfur compounds in comets and to understand sulfur chemistry during the Solar System formation.