Vibrationally induced photodetachment of electrons from negative molecular ions

An analytical theory is described for the vibrationally induced photodetachment of electrons from negative molecular ions with large dipole moments. The approach is based on the use of rotationally adiabatic potential curves which are obtained by diagonalizing a simple charge-dipole interaction potential. The mechanism of the vibrationally induced electron detachment is related to the crossing of an attractive rotationally adiabatic potential-energy curve for the vibrationally excited state with repulsive curves for the vibrational ground state of the parent molecule. A simple Franck-Condon theory is used to treat the curve crossing, and a formula for the linewidths in the photodetachment spectra is derived. An interesting prediction is that, for large values of the total angular momentum J, the linewidths decrease with increasing J. This finding is in agreement with recent experimental results for the photodetachment of electrons in PtN^-.