Nonadiabatic transition in the A-band photodissociation of ethyl iodide from 294 to 308 nm by using velocity imaging detection.

Photodissociation dynamics of ethyl iodide in the A-band is investigated at wavelengths between 294 and 308 nm using resonance-enhanced multiphoton ionization technique combined with velocity imaging detection. The I/I* branching, translational energy disposals, anisotropy parameters, and curve crossing probabilities of the dissociation channels are determined. The I(5p(2)P(3/2))-product channel is found to have hotter internal states of C(2)H(5), and the I*(5p(2)P(1/2)) channel is accompanied by colder C(2)H(5). Anisotropy parameters (beta) for the I* channel remain at 2.0, indicating that the I* production should originate from the (3)Q(0) state. The beta values are from 1.6 to 1.9 in the I-product channel, which comprises two components of direct excitation of (3)Q(1) and nonadiabatic transition between the (3)Q(0) and (1)Q(1) states. The curve crossing probability rises rapidly around the conical intersection but remains almost constant after passing through the curve crossing. The (1)Q(1) and (3)Q(0) states in the exit region are thus expected to cross almost parallel along the dissociation coordinate. As compared to the case of CH(3)I, the nonadiabatic transition probabilities are slightly enhanced by an ethyl-substituted group.