State-to-state reaction dynamics of CH3I photodissociation at 304 nm

The detailed reaction dynamics of CH3I photodissociation at 304 nm were studied by using high-resolution long time-delayed core-sampling photofragment translation spectroscopy. The vibrational state distributions of the photofragment, i.e., CH3, are directly resolved due to the high kinetic resolution of this experiment for the first time. CH3 radicals produced from I*((3)Q(0+)), I((1)Q(1) <- (3)Q(0+)), and I((3)Q(1)) channels are populated in different vibrational state distributions. The I*(3Q(0+)) and I((3)Q(1)) channels show only progressions in the nu(2)'(a(2)) umbrella bending mode, and the I((1)Q(1) <- (3)Q(0+)) channel shows both progression in the nu(2)' umbrella bending mode and a small amount of excitation in the nu(1)'(a,(1)') C-H stretching mode. The photodissociation processes from the vibrational hot band of CH3I (upsilon(3) = 1, upsilon(3) = 2) were also detected, primarily because of the absorption probability from the vibrational excited states, i.e., hot bands are relatively enhanced. Photofragments from the hot bands of CH3I show a cold vibrational distribution compared to that from the vibrational ground state of CH3I. The I* quantum yield and the curve crossing possibility were also studied for the ground vibrational state of CH3I. The potential energy at the curve crossing point was calculated to be 32 790 cm(-1) by using the one-dimensional Landau-Zener model.