Near threshold Cl-•CH3I photodetachment: Apparent 2P1/2 channel suppression and enhanced 2P3/2 channel vibrational excitation

Cl-center dot CH3I cluster anion photoelectron images are recorded over a range of detachment wavelengths in the immediate post threshold region. The photoelectron spectral features fall into two categories. A number of weak, photon energy dependent transitions are observed and attributed to atomic anion fragmentation products. Several more intense, higher electron binding energy transitions result from single photon cluster anion detachment. Comparison with I-center dot CH3I suggests that the detachment process is more complicated for Cl-center dot CH3I. The single photon transition spacing is consistent with CH3I nu(3) mode excitation, but the two distinct vibronic bands of I-center dot CH3I detachment are not easily distinguished in the Cl-center dot CH3I spectra. Similarly, while the spectral intensities for both cluster anions show non-Franck Condon behavior, the level of vibrational excitation appears greater for Cl-center dot CH3I detachment. These observations are discussed in terms of low lying electronic states of CH3I along the C-I coordinate, and the influence of the CH3I moiety on the neutral halogen atom states. (c) 2011 American Institute of Physics. [doi: 10.1063/1.3583812]