Production and IR absorption of cyclic CS2 in solid Ar

Linear carbon disulfide (denoted as SCS) isolated in solid N-2 or Ar at 13 K was irradiated with light at 193 nm from an ArF excimer laser. In addition to an absorption line of CS at 1277.4 cm(-1), new lines at 881.3 and 520.9 cm(-1) were observed after photolysis of SCS in solid N-2 These lines are assigned to cyclic CS2 (denoted cyc-CS2) based on results from S-34- and C-13-isotopic experiments. Doublet lines of cyc-CS2 at 876.5 (881.1) and 517.7 (522.7) cm(-1) were observed after irradiation of SCS in solid Ar at 193 nm; lines in parentheses are associated with a minor matrix site. Secondary photolysis at 248, 308, 532, 560, or 580 nm diminishes signals of cyc-CS2 and produces SCS. Theoretical calculations using MP2-full and density-functional methods (BLYP and B3LYP) predict three isomers of CS2: SCS, cyc-CS2, and linear CSS; relative energies, structures, vibrational wavenumbers, and LR intensities were predicted for each isomer. Cyc-CS2 has C-S bonds (similar to 1.74 Angstrom) elongated relative to those of SCS (similar to 1.56 Angstrom), a S-S bond similar to 2.14 Angstrom, and angle SCS approximate to 76 degrees; it lies similar to 73 kcal mol(-1) above SCS. Calculated vibrational wavenumbers, IR intensities, and isotopic shifts for cyc-CS2 fit satisfactorily with experimental results. An asymmetric transition state connecting SCS and cycCS(2) is characterized, yielding a ring-opening barrier of similar to 24.4 kcal mol(-1) (zero-point energy corrected). Photoconversion between linear and cyclic CS2 in a matrix cage is discussed.