Bound rovibronic levels of the [formula omitted] complex

Abstract

We have used ab initio MRCI (multireference internally contracted configuration interaction) potential energy functions to compute the energies of the bound rovibronic levels of the T-shaped nearly-degenerate electronically excited HeN 2 +(A 2Π) . In these calculations a variational approach which includes the rotation-vibration, the electronic angular and spin momenta couplings has been employed. The wavenumbers for the large amplitude bending and stretching modes have been calculated to lie around 60 and 75 cm −1, respectively. For J = 1 2 , three states with excited bending and one state with excited stretching mode were found to be bound. The weak interaction between He and the N 2 + (A 2Π u) state leads to a spin flip. The inverted doublet in N 2 + (A 2Π u) becomes a normal doublet in the complex. This unusual effect is attributed to large anisotropies and to a large difference potential between the A′ and A″ components, which leads also to the largest known parity splittings in Renner-Teller weakly bound complexes.