Selective dissociation pathways induced by local electronic excitation of molecules in the gas phase and adsorbed on surfaces

The goal is to investigate how local electronic excitation of a polyatomic molecule can result in selective decomposition channels over other energetically allowed ones. In the proposed work, we study the generality of using direct excitation to an excited potential energy surface repulsive in a specific bond to induce fission of that bond, an excitation found to be selective in CH2BrI photodecomposition. In addition two new excitation mechanisms for controlling chemical fragmentation, are investigating the role of triplet states in promoting fission to radical products over molecular elimination and the efficacy of using electronic excitation localized on a particular functional group to favor dissociation at or near that group. The experimental technique utilized, measurement of photofragment velocity and angular distributions by the cross laser-molecular beam time-of-flight technique, incorporates specific capabilities necessary for identifying all the primary dissociation channels resulting from local electronic excitation. The work is fundamental to understanding and controlling reactions of isolated polyatomic molecules both in tha gas phase and absorbed on surfaces. The first year and a half of the grant period involves the dedicated construction of the high resolution crossed laser molecular beam time of flight apparatus for these studies.