Photofragment translational spectroscopy of CH3I at 225 nm—with the high excitation of the symmetric stretch vibration of CH3 fragment

The photodissociation dynamics of CH3I 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 3Q0, 3Q0 ← 1Q1, 1Q1, and 1Q1 ← 3Q0, are obtained with both the symmetric stretch (ν1) and the umbrella (ν2) vibrational modes of the CH3 fragments partially resolved. The strong excitation of the symmetric stretch mode (ν1) is revealed in both the I and the I* channels. The branching fractions for the four pathways (0.09 for 3Q0, 0.03 for 3Q0 ← 1Q1, 0.34 for 1Q1, and 0.54 for 1Q1 ← 3Q0) show that the parallel transition (3Q0 ← X) is the major and the I channel is dominant in the photodissociation of CH3I at 225 nm. The curve-crossing probability is found to be 0.86 for 1Q1 ← 3Q0 but 0.08 for 3Q0 ← 1Q1.