Dynamic model and tunneling splittings in LMH4 non-rigid hydrides

A non-rigid model for the molecules LiBH₄. NaBH₄⁺. LiCH₄⁺ is suggested on the basis of ab initio data. The model is used in numerical calculations of the levels of large-amplitude deformation-migration motion of the cation in these molecules. It is shown that the lowest states can be regarded as highly anharmonic bending vibrations, while levels above the barrier should be considered as hindered rotation of the MH₄ group. T_d symmetry is used to classify the states. Tunneling splittings of the vibrational states are 0.01–1 cm^?1.