Spectroscopic observation of vibrational Feshbach resonances in near-threshold photoexcitation of X− ·CH3NO2 (X−=I− and Br−)
Abstract
We report the observation of resonance structure in the absorption and X−/NO2− photofragment action spectra of the X−·CH3NO2 (X−=I− and Br−) complexes in the region above the electron detachment threshold. The resonance structure corresponds to peaks which appear at the onsets for vibrational excitation of the –NO2 wag, scissors, and stretch modes of neutral CH3NO2, the modes which most strongly distort upon electron capture into its π* lowest unoccupied molecular orbital. We attribute the peaks to excitation of vibrational Feshbach resonances of the CH3NO2− transient negative ion, where near-threshold excitation of X−·CH3NO2 spectroscopically accesses states of the free electron–CH3NO2 system.