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

Adiabatic potential energy surfaces are calculated for the ground and first excited electronic states of HeH2+ including their respective lowest dissociation limits: HeH2+(X̃ 2A′)→He(1S)+H2+(X̃ 2Σg+) and HeH2+(Ã 2A′)→He+(2S)+H2(X̃ 1Σg+). 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.