Site specific dissociation dynamics of propane at 157 nm excitation

Abstract

Photodissociation of propane at 157 nm excitation has been investigated using the photofragment translational spectroscopic (PTS) technique. Three dissociation channels have been experimentally observed: the atomic hydrogen (H) elimination, the molecular hydrogen (H2) elimination, and the methyl radical (CH3) elimination. Product translational energy distributions have been measured and relative branching ratios have also been estimated, which indicate that all these three processes are significant. The site effects on the H and H2 elimination have been quantified by investigating the photodissociation of the four propane isotopomers: CH3CD2CH3, CD3CH2CD3, CH2DCH2CH2D, and CD3CD2CD3. Experimental results indicate that the yield of the H elimination from the two terminal CH3 groups (terminal-H elimination) is larger than that from the internal CH2 group (internal-H elimination). H2 elimination from the internal carbon atom of propane (2,2-H2 elimination) is the dominant process while H2 elimination channels from the vicinal carbon atoms (1,2-H2 elimination) are less significant. Minor processes of H2 elimination from terminal carbon atoms (1,1-H2 and 1,3-H2 elimination) were also observed. The translational energy distributions also show that the dynamics of H and H2 elimination from different sites are significantly different. Relative branching ratios of H and H2 elimination processes from different sites have also been determined.