| The rotation-vibration states of the linear He(,2)H('+) and He(,2)D('+) molecules are investigated by an ab initio variational approach with the Hamiltonian recently derived by Estes and Secrest through direct coordinate transformation method. Various forms of this Hamiltonian for a linear triatomic molecule are presented. The potential energy function for the He(,2)H('+) and He(,2)D('+) molecules is expanded in terms of power series of local functions of internal coordinates. These results show strong mixing between the vibrational modes, especially between symmetric stretch and bend modes for He(,2)H('+). The effect of the motion of the nuclei on the binding energy are examined by calculating the zero point energies in the diatomics and triatomics. It is found that the zero point energy contribution destabilizes the binding in both systems and He(,2)D('+) is more stable than He(,2)H('+) by about 1.0 KJ/mol. Second order perturbation calculations are also carried out for both systems with the potential expanded to fourth order of internal coordinates. The perturbation results are surprisingly in good agreement with the accurate variational results for a few low-lying states. |
