Photodissociation of HOD (ν_OD=3): Demonstration of preferential O-D bond breaking

It has been predicted that photodissociation of vibrationally excited HOD may preferentially yield either OD+H or D+OH, depending on the vibrational mode and the dissociation wavelength. To date, only the former preference has experimentally been demonstrated. In the present work preferential O-D bond breaking has been achieved from the photolysis of HOD (ν_OD=3) at 193 nm. HOD was prepared in a specific rovibrational level of the second overtone of the O-D stretch via infrared excitation. The subsequent photolysis led to enhancement of both OH and OD production, the OH/OD branching ratio being 2.6±0.5. The results agree with the predictions of Imre and co-workers [J. Phys. Chem. 93, 1840 (1989)] on the enhancement of ν_OD≥3 photodissociation but differ in the branching ratio obtained at the specific photolysis wavelength.