O–D bond dissociation from the 3s state of deuterated hydroxymethyl radical (CH2OD)

The photodissociation of the deuterated hydroxymethyl radical CH2OD is investigated on the lowest excited state, the 3s Rydberg state, in the wavelength region 365–318 nm where the D atom is the only significant product. The translational energy distribution and kinetic energy-dependent anisotropy parameter of the D channel are determined by the core-sampling time-of-flight technique at 352.5 nm. The negative recoil anisotropy parameter βeff=−0.7±0.1 is consistent with the perpendicular nature of the transition from the ground state. The fraction of the available energy partitioned into the translational degree of freedom is 0.69. Ground state products CH2O (1 1A1)+D constitute the main photodissociation channel, and no significant H product is detected at these wavelengths. Comparison with the conical intersection calculations of Hoffman and Yarkony suggests that O–D bond rupture involves crossing from the 3s potential energy surface to a repulsive region of the ground state surface at a large O–D bond distance. Isomerization of CH2OD to CH2DO is not competitive with the fast O–D dissociation.