Infrared absorption of gaseous ClCS detected with time-resolved Fourier-transform spectroscopy.
A transient infrared absorption spectrum of gaseous ClCS was detected with a step-scan Fourier-transform spectrometer coupled with a multipass absorption cell. ClCS was produced upon irradiating a flowing mixture of Cl2CS and N2 or CO2 with a KrF excimer laser at 248 nm. A transient band in the region of 1160-1220 cm-1, which diminished on prolonged reaction, is assigned to the C-S stretching (nu1) mode of ClCS. Calculations with density-functional theory (B3P86 and B3LYP/aug-cc-pVTZ) predict the geometry, vibrational wave numbers, and rotational parameters of ClCS. The rotational contour of the spectrum of ClCS simulated based on predicted rotational parameters agrees satisfactorily with experimental observation; from spectral simulation, the band origin is determined to be at 1194.4 cm-1. Reaction kinetics involving ClCS, CS, and CS2 are discussed.
Energies, structures, and vibrational frequencies of FCS and CICS
Abstract The energies, geometries, and vibrational frequencies of the experimentally uncharacterized fluorothioformyl, FCS, and chlorothioformyl, ClCS, radicals are predicted from ab initio theory. Theoretical results for the thiocarbonyl halides, F 2 CS and Cl 2 CS, are presented for calibration of the methods against experiment. Spin contamination in the unrestricted Hartree—Fock (UHF) wavefunctions of the radicals caused difficulties with the predictions of structures and vibrational frequencies at the UHF and unrestricted second-order Moller—Plesset (UMP2) levels.
Dynamics of the second excited singlet state of thiophosgene in solution
Abstract The dynamic behavior of the second excited singlet state of Cl 2 CS has been investigated for the first time in liquid solutions. In perfluoroalkane solvents strong B-X fluorescence (φ f 0 up to 0.077) is observed when the molecule is excited to bound vibrational states. B lifetimes of up to 2.8 ns are obtained. Dissociation, either directly (in competition with vibrational relaxation) at high vibrational energies or indirectly by solvent activation when low vibrational levels are initially populated, appears to be the main radiationless decay path. Fluorescence is much weaker in other solvents. A rate constant of 9.5 × 10 9 M −1 s − is measured for quenching by n -hexane.