Isomers of OCS2: IR absorption spectra of OSCS and O(CS2) in solid Ar.

Irradiation of an Ar matrix sample containing O(3) and CS(2) with a KrF excimer laser at 248 nm yielded new lines at 1402.1 (1404.7), 1056.2 (1052.7), and 622.3 (620.5) cm(-1); numbers in parentheses correspond to species in a minor matrix site. Secondary photolysis at 308 nm diminished these lines and produced mainly OCS and SO(2). Annealing of this matrix to 30 K yielded a second set of new lines at 1824.7 and 617.8 cm(-1). The first set of lines are assigned to C=S stretching, O-S stretching, and S-C stretching modes of carbon disulfide S-oxide, OSCS; and the second set of lines are assigned to C=O stretching and OCS bending modes of dithiiranone, O(CS(2)), respectively, based on results of (34)S- and (18)O-isotopic experiments and quantum-chemical calculations. These calculations using density-functional theory (B3LYP/aug-cc-pVTZ) predict four stable isomers of OCS(2): O(CS(2)), SSCO, OSCS, and SOCS, listed in order of increasing energy. According to calculations, O(CS(2)) has a cyclic CS(2) moiety and is the most stable isomer of OCS(2). OSCS is planar, with bond angles angle OSC congruent with 111.9 degrees and angle SCS congruent with 177.3 degrees ; it is less stable than SSCO and O(CS(2)) by approximately 102 and 154 kJ mol(-1), respectively, and more stable than SOCS by approximately 26 kJ mol(-1). Calculated vibrational wave numbers, IR intensities, (34)S- and (18)O-isotopic shifts for OSCS and O(CS(2)) fit satisfactorily with experimental results.