Vibrational dynamics of the CH4·F- complex.

Motivated by recent photodetachment experiments studying resonance structures in the transition-state region of the F + CH(4) → HF + CH(3) reaction, the vibrational dynamics of the precursor complex CH(4)·F(-) is investigated. Delocalized vibrational eigenstates of CH(4)·F(-) are computed in full dimensionality employing the multiconfigurational time-dependent Hartree (MCTDH) approach and a recently developed iterative diagonalization approach for general multiwell systems. Different types of stereographic coordinates are used, and a corresponding general N-body kinetic energy operator is given. The calculated tunneling splittings of the ground and the lower vibrational excited states of the CH(4)·F(-) complex do not significantly exceed 1 cm(-1). Comparing the converged MCTDH results for localized vibrational excitations with existing results obtained by normal-mode-based (truncated) vibrational configuration interaction calculations, significantly lower frequencies are found for excitations in the intermolecular modes.