Adiabatic separations of the vibrational motions in HeH2(+) and the calculation of metastable states

Recent ab initio calculated potential energy data for the ground electronic state of HeH2(+) are used to construct a new potential function, which is suitable to describe the interaction between He and H2(+) at low collision energies. All bound and the lowest quasi-bound rotation-vibrational levels of HeH2(+) are evaluated within the framework of the Sutcliffe-Tennyson Hamiltonian for triatomic molecules neglecting Coriolis interactions between the states. Adiabatic separations of the vibrational motions are used to simply the calculation of the bound and quasi-bound levels close to the dissociation limit. Comparison with the results of full-dimensional calculations shows that a very good agreement is obtained when separating adiabatically the high-frequency H2(+) stretching motion from the remaining two low-frequency modes and that further separation of the low-frequency motions still provides useful approximations for the positions of the bound and lowest quasi-bouns states.