Mechanistic study of the photoexcitation, photoconversion, and photodissociation of CS2.

Carbon disulfide is a prototype molecular system for studies of photophysical processes in molecules at different time scales and is also relevant to astrophysics. Here, reliable molecular properties are computed for linear SCS, bent cyc-CS2, and linear CSS forms using highly correlated post Hartree-Fock methods in conjunction with large basis sets. Structures are identified using explicitly correlated and standard coupled cluster techniques. Evolution of the lowest-lying singlet and triplet electronic states of the three isomers along the SS and CS stretching coordinates and along the bending angle are mapped at the multireference configuration interaction (MRCI)/aug-cc-pV(5+d)Z level of theory. The computations suggest that the 1B2(1Σ+) electronic state of the SCS isomer plays an important role in the photoconversion of CS2 to cyc-CS2 and CSS. Photoconversion competes with photodissociation. Plausible mechanisms for the production of S2 and CS diatomics after the photoexcitation of SCS are proposed. To aid in the identification of CSS in the laboratory and in astrophysical media, a set of spectroscopic constants and rovibrational levels for CSS are reported.