Ab initio theory and rotational spectra of linear carbon chains SiCnS

Abstract

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 Si29, S34, and both C13 isotopic species of SiC2S have been detected, allowing the determination of both an effective r0 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 v1 and v2, and to a progression in the second lowest-frequency bending mode v4 up to 3v4. Equilibrium structures and various spectroscopic properties are predicted for all SiCnS species with n=1–8.