C3S - A MOLECULE OF INTEREST TO INTERSTELLAR CLOUD CHEMISTRY

Various spectroscopic properties (force constants, vibrational frequen cies, vibration-rotation coupling constants, 1-type doubling constants , centrifugal distortion constants and IR intensities) have been calcu lated for the interstellar molecule C3S (3-thioxo-1,2-propadienylidene ). An accurate equilibrium geometry has been determined by combination of experimental and theoretical data: R1e(C(1)C(2)) = 1.2800 angstrom , R2e(C(2)C(3)) = 1.2936 angstrom and R3e(C(3)S) = 1.5363 angstrom. Th e equilibrium dipole moment is predicted to be 3.89 D from coupled clu ster theory with single and double excitation operators plus a quasi-p erturbative treatment of connected triple substitution (CCSD(T)) calcu lations with a basis set of 160 contracted gaussian-type orbitals. The experimental ground-state value of 2.81(7) D appears to be substantia lly too small. Calculated wavenumbers of stretching vibrational transi tions for C3S and isotopomers are in very good agreement with the resu lts from matrix-isolation IR spectroscopy.