Magnetic Susceptibility Anisotropy, Molecular Quadrupole Moment, and the Sign of the Electric Dipole Moment in OCCCS: A High-Resolution Microwave Fourier Transform Study Combined with IGLO Calculations

Abstract

The molecular Zeeman effects of 16O12C12C12C32S and 16O12C12C12C34S have been observed by microwave Fourier transform spectroscopy in magnetic fields up to 20 000 G. The magnetic susceptibility anisotropy of the OCCCS molecule is ξ||-ξ⊥ = −18.740(6) 10−6 erg G−2 mol−1. The molecular g⊥ values for the two isotopomers obtained from the J = 3 → J = 2 transitions are g⊥(32S) = −0.013604(14) and g⊥(34S) = −0.013370(30). These data yield the sign of the molecular electric dipole moment which has −OCCCS+ polarity. Combining g⊥ and the rotational constant B gives the molecular electric quadrupole moment referred to the molecular center of mass as Q||(16O12C12C12C32S) = −1.97(3) DÅ. For ξ||-ξ⊥ ab initio calculations were carried out by the IGLO method. Their results compare well with the experimental value, although the system seems to be unusually demanding as can be seen from the untypical slow convergence of the result with increasing basis set size. Conventional coupled Hartree-Fock calculations with moderately sized basis sets are approximately 200 units off the experimental value. Comparative calculations on tricarbonoxide show that the basis set dependency is much less pronounced in this molecule.