Photofragment translational spectroscopy of CH_3I at 225 nm-with the high excitation of the symmetric stretch vibration of CH_3 fragment

摘要

The photodissociation dynamics of CH_3I at 225 nm is studied on our high resolution mini-TOF photofragment translational spectrometer. The photofragment translational spectra of the I and the I channels via parallel and perpendicular transitions, i.e., of the four pathways ~3Q_0, ~3Q_0 ← ~1Q_1, ~1Q_1, and ~1Q_1 ← ~3Q_0, are obtained with both the symmetric stretch (ν_1) and the umbrella (ν_2) vibrational modes of the CH 3 fragments partially resolved. The strong excitation of the symmetric stretch mode (ν_1) is revealed in both the I and the I channels. The branching fractions for the four pathways (0.09 for ~3Q_0, 0.03 for ~3Q_0 ← ~1Q_1, 0.34 for ~1Q_1, and 0.54 for ~1Q_1 ← ~3Q_0) show that the parallel transition (~3Q_0 ← X) is the major and the I channel is dominant in the photodissociation of CH 3I at 225 nm. The curve-crossing probability is found to be 0.86 for ~1Q_1 ← ~3Q_0 but 0.08 for ~3Q_0 ← ~1Q_1.