The low-lying electronic states and harmonic vibrational frequencies of HCB, HBC, HCB- and HBC-

摘要

The low-lying singlet and triplet states of HCB and HBC, and doublet states of HCB" and HBC" are examined using ab initio molecular orbital theory at the HF/TZPP, FOCI/MCSCF level. For the neutral molecules, several new low-lying electronic stales are found, and the linear triplet structures are found to have the lowest energy. For the anions, the V states arc lower in energy than the 2n stales. For HCB, the 3n state is 15.38 kcalmol"1 more stable than the 3E~ stale, und for HBC the1II is 2.51 kcal mol"1 below the 1S" state at the first order configuration interaction (FOCI) level. 'Diebarriers to conversion orHBC(3ri) to HCD(3II), HBC('A('A,)) to HCB('A'C,) and HBC('A('A2)) to HCB(!A" C,) arc 23.21,12.97 and 21.09 kcal mol"1, respectively. The activation energies to conversion of HBC"(2S*) to HCB~and HCB"(211) to HBC~(2II) are 18.13 and 25.88 kcabnol, respectively. The energies of fragmentation of HCB and HBC, and the harmonic vibrational frequencies of the neutral molecules and the anions are also reported to provide information for the possible experimental observation of these species.