Nonadiabatic dynamics in the photodissociation of ICH2CN at 266 and 304 nm studied by the velocity map imaging

Photodissociation dynamics of iodoacetonitrile (ICH2CN) have been investigated at pump wavelengths of 266 and 304nm using a photofragment ion image velocity mapping technique. At both wavelengths, the prompt C–I bond rupture takes place on the repulsive excited states to give I(P3∕22) and I*(P1∕22), and their speed and spatial distributions are simultaneously measured. The recoil anisotropy parameter (β) at 266nm is determined to be 1.10 and 1.60 for I and I*, respectively, while it is found to be much higher at 304nm to give β=1.70 and 1.90 for I and I*, respectively. The branching ratios for I*∕I channels are measured to be 0.724 and 0.136 at 266 and 304nm, respectively, giving insights on nonadiabatic transition phenomena and relative oscillator strengths of optically accessible transitions of ICH2CN. Accordingly, relative oscillator strengths of parallel/perpendicular transitions and nonadiabatic transitions among the excited states are quantitatively characterized. A large portion of the available en...