Bound and low-lying quasi-bound rotation-vibration energy levels of the ground and first excited electronic states of HeH2+

Adiabatic potential energy surfaces are calculated for the ground and first excited electronic states of HeH2+ including their respective lowest dissociation limits: HeH2+((X) over tilde (2)A') --> He(S-1) + H-2(+)((X) over tilde (2)Sigma(g)(+)) and HeH2+((A) over tilde (2)A') --> He+(S-2) + H-2((A) over tilde (1)Sigma(g)(+)). Using the Sutcliffe-Tennyson Hamiltonian for triatomic molecules, the energies of the rotation-vibration bound states are determined variationally and the energy positions and widths of low-lying quasi-bound resonance states are obtained applying the stabilization method. For the excited electronic state a number of resonances are predicted which have considerably long lifetimes and can therefore be expected to be important for a detailed description of the chemical reactivity of the HeH2+ ion. The positions of these resonance states are shown to coincide closely with the eigenvalues of an approximate Hamiltonian derived when applying the concept of the Born-Oppenheimer adiabatic separation to the nuclear vibrational motions with different energy contents. (C) 2002 Elsevier Science B.V. All rights reserved.