Isotope Effects in Two-Body Photodissociation Channels of CHD₃ at 118 nm

The photodissociation dynamics of CHD₃ at 118 nm was investigated by the time-sliced velocity map imaging (VMI) technique, and the momentum and anisotropy parameter (β) distributions of isotope-distinctive two-body fragments (CD₃, CHD₂, CD₂, and CHD) were mapped out. Pronounced isotope effects in CD₃+H and CHD₂+D channels were revealed. Peculiar bulge-like features were observed in the anisotropy parameter (β) distributions of CD₃ and CD₂ fragments, suggesting that several fragmentation pathways proceed with different signs of β-values. Through careful analysis of the TKER (total kinetic energy release) and β distributions, the primary source of this isotope effect can be ascribed to one of the dissociation pathways mediated by S₁-S₀ internal conversion. The momentum distributions of CD₂ and CHD were partitioned into two-body and three-body dissociation channels, with minor contributions from the latter. Again, the momentum-dependent β-distributions are highly sensitive to isotopic substitutions. This work highlights the strong isotope effects manifested in the dynamical attributes of two-body photodissociation channels of CHD₃ at 118 nm, and thus provides invaluable clues for understanding the underlying mechanisms.