A slice imaging and multisurface wave packet study of the photodissociation of CH3I at 304 nm

The role of the conical intersection between the (1)Q(1) and (3)Q(0) excited states in the photodissociation of CH3I at 304 nm is investigated drawing a comparison between the adiabatic-through direct absorption to the (3)Q(1) state-and non-adiabatic-via the (1)Q(1) -> (3)Q(0) conical intersection-production of I atoms in the ground P-2(3/2) state. The versatility of the slice imaging technique in combination with resonance enhanced multiphoton ionization (REMPI) detection of I(P-2(3/2)) atoms allow distinct measurements of the competing processes. The I(P-2(3/2)) atom kinetic energy distributions (KEDs) obtained in both cases reflect inverted vibrational progressions of the nu(2) umbrella mode of the CH3 co-product. The experimental results show a satisfactory agreement with multisurface wave packet calculations using a reduced dimensionality (pseudotriatomic) model carried out on the available ab initio potential energy surfaces.