General Anharmonic Force Constants of Carbon Disulfide

Twelve force constants in the general quartic force field of carbon disulfide have been determined by a least-squares method from the available spectroscopic data on four isotopic species of carbon disulfide: 12C32S2, 13C32S2, 12C32S34S, and 13C32S34S. A reasonable set of force constants is obtained together with a set of the third-order parameters λ1, λ2, λ3, and δ which appear in Fermi coupling off-diagonal matrix elements. From the converged set of force constants, l-type doubling constants for a few π-vibrational states are calculated through a direct numerical diagonalization method of vibrational Hamiltonian matrix. They agree well with the observed l-type doubling constants.