Abstract

Photofragment imaging is used to study the internal state and velocity distributions of methyl fragments following photodissociation of CD₃I molecules by 266-nm radiation. The molecular fragments are state selectively ionized via 2 + 1 resonance enhanced multiphoton ionization (REMPI) through the 3p_z Rydberg state of methyl. The photofragment imaging technique,^1,2 which records the entire velocity distribution for the state selectively ionized fragment, allows us to record the velocity distribution of the ionized photofragments for every laser pulse. Because the methyl fragment is state selectively ionized by the REMPI process, and the parent methyl iodide molecule is cooled in a molecular beam, the velocity of the ion mirrors the internal state distribution of the iodine atom born in coincidence with the selected state of the methyl. For a selected state of the methyl radical two velocities are seen. The faster fragments are bom in coincidence with ground state iodine l(²P_3/2), and the slower fragments are born in coincidence with excited state iodine I(²P_1/2). The intensity ratio of fast to slow methyl fragments is then unique to each internal state of the methyl fragment and is used to help assign the methyl REMPI spectrum. This is illustrated in the spectra shown in Fig. 1 in which there are two overlapping bands.

© 1989 Optical Society of America