Ab initio SCF and CI study of the HCS +-CSH + system: Potential surfaces for hydrogen abstraction and internuclear bending For ground and excited states and vertical spectrum for HCS +

Abstract

Ab initio SCF and configuration interaction calculations of the multi-reference double-excitation (MRD-CI) type are reported for the HCS +-CSH + system using two different basis sets of double-zeta plus polarization quality. Potential surface calculations find an absolute minimum for linear HCS + with CS = 2.814 a o and CH = 2.062 a o but only a saddle point for the corresponding CSH + species, lying 110 kcal/mole above the most stable HCS + structure. Because of large distinctions in the minimum IP's of CS and CO it is seen that the HCS + ground state decomposes into CS +( 2Σ +) + H( 2S) whereas the corresponding products for HCO + are proton plus CO( 1Σ +); similar differences are noted among their excited state products. The lowest excited states of HCS + are found to be (π,π*) species with nearly the same ground state transition energies as in CS, while the corresponding 3,1 Π(σ,π*) species lie considerably higher in HCS + as a result of the effects of σ MO stabilization relative to the unprotonated diatomic species. Comparison with the appropriate quantities for the HCO +-COH + system is made wherever possible and qualitative arguments are given to rationalize the distinctions which occur. The heat of formation is calculated to be approximately 25 kcal/mole higher for HCS + than for HCO +.