Dynamics of atomic and molecular hydrogen elimination from small alkanes following 157-nm excitation

Photodissociation of a series of C-3-C-9 akanes following 157 nm excitation has been investigated using the photofragment translational spectroscopy ( PTS) technique. Three series of alkanes, normal alkanes, branched alkanes, and cyclic alkanes, were studied and the atomic hydrogen (H) and molecular hydrogen (H-2) elimination from their photodissociation were experimentally investigated. Experimental results show that the dynamics of the H and H-2 elimination processes from larger n-alkanes is quite similar to that of pr opane. Dissociation of the branched alkanes is, however, significantly diff erent from that of the normal alkanes. C-C bond fission is more significant in the branched alkanes. There are also notable differences among the bran ched alkanes for the H and H-2 elimination processes. Photodissociation dyn amics of small cyclic alkanes are significantly different from that of the acyclic alkanes. This is likely due to their significantly different electr onic structures caused by the large ring strain in small cyclic alkanes. Th e H and H-2 elimination channels for larger cyclic alkanes are quite simila r to the normal alkanes. Relative branching ratios of the H and H-2 elimina tion channels for all the alkane molecules are determined and compared.