HCB和HCB^-的激发态光谱与态-态转化的理论研究

Theoretical Studies of Spectra of the Excited States and Conversion Barriers of a State to State for HCB and HCB^-

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/TZP, FOCI/MCSCF level. For the neutral molecules, several new low-lying electroinc states are found, and the linear triplet structures are found to have the lowest energy. For the anions, the 2 ∑+ states are lower in energy than the 2Π states. For HCB, the 3Π state is 15.38kcal·mol-1 more stable than the 3∑- state, and for HBC the 3Π is 2.51kcal·mol-1 below the 3∑- state at the first order configuration interaction (FOCI) level. The barriers of the conversion of HBC(3Π) to HCB(3Π), HBC(1△(1A1)) to HCB(1A’C3) and HBC(1△(1A2)) to HCB(1A"C3) are 23.21, 12.97 and 21.09kcal·mol-1,respectively. The activation energies of the conversion of HBC-(2∑+) to HCB(2∑+) and HCB-(2Π) to HBC-(2Π) are 18.13 and 25.88kcal·mol-1, respectively. A symmetry breaking phenomenon is observed in several states. 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.