THEORETICAL INVESTIGATION OF THE RELATIVE STABILITIES OF SINGLET AND TRIPLET DISULFIDES

Ab initio molecular orbital calculations have been performed on the singlet (1A) and triplet (3A(u)) states of hydrogen persulfide (HSSH) at the SCF and post-SCF levels using a double zeta basis set augmented with polarization functions. The relative energies for this system were computed by many-body perturbation theory (MBPT) and coupled-cluster (CC) methods, indicating that the singlet and triplet states are both lower in energy than the isolated HS fragments. Structural information for 1[HSSH] determined at the SCF and post-SCF levels are in good agreement with experiment. The triplet state is very weakly bound (< 5 kcal/mol) and lies approximately 50 kcal/mol above the singlet state.