Ab initio theory and rotational spectra of linear carbon chains SiCnS

On the basis of extensive coupled cluster calculations, the rotational spectra of the linear silicon- and sulfur-containing carbon chains SiC2nS (n=1-3) in their singlet electronic ground state and SiC3S in its triplet electronic ground state have been detected and characterized by means of molecular beam Fourier transform microwave spectroscopy. Rotational and centrifugal distortion constants have been determined to high accuracy as well as the spin-spin coupling constant for triplet SiC3S. In addition, the Si-29, S-34, and both C-13 isotopic species of SiC2S have been detected, allowing the determination of both an effective r(0) structure, as well as a mixed experimental-theoretical structure resulting from the combination of the measured rotational constants with the vibration-rotation coupling constants calculated ab initio. Several rotational satellite lines have also been observed for SiC2S and, on the basis of their predicted vibration-rotation and l-type doubling constants, were assigned to the two highest-frequency stretching modes v(1) and v(2), and to a progression in the second lowest-frequency bending mode v(4) up to 3v(4). Equilibrium structures and various spectroscopic properties are predicted for all SiCnS species with n=1-8. (C) 2002 American Institute of Physics.