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

Abstract

The role of the conical intersection between the ¹Q₁ and ³Q₀ excited states in the photodissociation of CH₃I at 304 nm is investigated drawing a comparison between the adiabatic—through direct absorption to the ³Q₁ state—and non-adiabatic—via the ¹Q₁ → ³Q₀ conical intersection—production of I atoms in the ground ²P_3/2 state. The versatility of the slice imaging technique in combination with resonance enhanced multiphoton ionization (REMPI) detection of I(²P_3/2) atoms allow distinct measurements of the competing processes. The I(²P_3/2) atom kinetic energy distributions (KEDs) obtained in both cases reflect inverted vibrational progressions of the ν₂ 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.