Ab initio potential energy curves for low-lying states of carbon disulfide

Abstract

Potential energy surfaces for the ground singlet (S0), lowest excited singlet (S1), and lowest triplet (T0) electronic states of carbon disulfide are explored using ab initio Hartree–Fock (HF), generalized valence bond (GVB) and multiconfiguration self-consistent-field (MCSCF) methods using the 6-31G* basis. The lowest singlet hypersurface, S0, contains the linear (D∞h) equilibrium geometry ground state X 1Σ+g and the previously unreported bent (C2v) conformer 1A1. The calculated geometry of the linear state [re(C–S)=1.544 Å] compares favorably with experiment [r0(C–S)=1.556 Å]; there are no experimental values to compare with the calculated geometry of the bent state [re(C–S)=1.718 Å, <SCS=78.4°]. The transition state between the linear and bent conformers is determined to have C2v geometry [r(C–S)=1.691 Å, <SCS=103.4°] and a barrier height of 7.7 kcal/mol. We also explore the 1B2 surface, S1, and the 3B2 surface, T0, finding the equilibrium geometry, dipole moments, and vibrational frequencies of these states as well as those of the ground state and bent conformer.