Near threshold Cl^-·CH₃I photodetachment: Apparent ²P_1/2 channel suppression and enhanced ²P_3/2 channel vibrational excitation

Cl^-·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^-·CH₃I suggests that the detachment process is more complicated for Cl^-·CH₃I. The single photon transition spacing is consistent with CH₃I ν₃ mode excitation, but the two distinct vibronic bands of I^-·CH₃I detachment are not easily distinguished in the Cl^-·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^-·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.