New data on photochemistry of the interstellar molecule: HNCS. Identification of the S···HCN complex.

Phototransformations of isothiocyanic acid (HNCS) induced by tunable UV laser were studied in low-temperature matrices. Two isomers of the precursor HNCS molecule are formed during UV irradiation of HNCS/Ar and HNCS/N2 samples: thiocyanic acid (HSCN) and isothiofulminic acid (HSNC). In addition, a complex between hydrogen cyanide and a ground state ((3)P) sulfur atom appears at irradiation with wavelength λ < 290 nm. The vibrational bands of the SHCN complex are observed at 3217.0 and 746.5 cm(-1) in Ar and 3223.5 and 764.5/752.0 cm(-1) in N2. At the beginning of irradiation SHCN is produced from the HNCS precursor. At longer times the main sources of the complex are HSCN and HSNC species. In solid nitrogen, HCN monomers are observed besides SHCN, indicating efficient escape of atomic sulfur out of the matrix cage occupied by the precursor. Differences in the extent of the observed processes are discussed in relation to the wavelength of the UV radiation applied and the type of matrices. Results of the computational studies on the SHCN geometry and infrared spectra are presented and compared with experimental data.