Photofragment imaging: The 266-nm photolysis of CD sub 3 I

Internal state and velocity distributions of methyl fragments from the 266-nm photodissociation of CD{sub 3}I in a supersonic beam are measured by using photofragment imaging. Methyl radicals are state-selectively ionized by using (2+1) resonance-enhanced multiphoton ionization (REMPI) via the 3p{sub z} Rydberg state, and the imaging technique records the velocity distribution of the ions. A line-by-line rotational analysis of the 3p{sub z}{l arrow}{tilde X} 0{sup 0}{sub 0} band, including conservation of the parent molecule's ortho:para ratio in the planar fragment molecules, indicates that about 90 cm{sup {minus}1} of rotational excitation about a C{sub 2} axis in CD{sub 3} results from the photolysis. The photodissociation appears to conserve the initial (low) rotational excitation about the C{sub 3} axis of the (cold) parent molecule. From the previously derived 3p{sub z}-{tilde X} Franck-Condon factors the branching ratio for the v = 2/v = 0 levels of the umbrella mode is determined to be 1.15 {plus minus} 0.13.