Isotope substitution in the expanded local mode approach: XH₂ → XHD molecules

In a previous paper (O.N. Ulenikov, R.N. Tolchenov, and Qing-shi Zhu, 1996, Spectrochimica Acta Part A, 52, 1829) we have described the 'expanded local mode' approach which is a considerable extension of the well-known local mode model (M.S. Child and L. Halonen, 1984, Adv. Chem. Phys 57, 1). We report here further extension of the 'expanded local mode' approach and consider, for the case of light atoms, the effects of isotopic substitution on the properties of the Hamiltonian and the spectroscopic parameters. For the XY₂ molecules of (C_2v) symmetry, it is shown that by analyzing the properties of the transformation coefficients, one can obtain relations between the parameters for different isotopomers.