Site specific dissociation dynamics of propane at 157 nm excitation

Photodissociation of propane at 157 nm excitation has been investigated usi ng the photofragment translational spectroscopic (PTS) technique. Three dis sociation channels have been experimentally observed: the atomic hydrogen ( H) elimination, the molecular hydrogen (H-2) elimination, and the methyl ra dical (CH3) elimination. Product translational energy distributions have be en measured and relative branching ratios have also been estimated, which i ndicate that all these three processes are significant. The site effects on the H and H-2 elimination have been quantified by investigating the photod issociation of the four propane isotopomers: CH3CD2CH3, CD3CH2CD3, CH2DCH2C H2D, and CD3CD2CD3. Experimental results indicate that the yield of the H e limination from the two terminal CH3 groups (terminal-H elimination) is lar ger than that from the internal CH2 group (internal-H elimination). H-2 eli mination from the internal carbon atom of propane (2,2-H-2 elimination) is the dominant process while H-2 elimination channels from the vicinal carbon atoms (1,2-H-2 elimination) are less significant. Minor processes of H-2 e limination from terminal carbon atoms (1,1-H-2 and 1,3-H-2 elimination) wer e also observed. The translational energy distributions also show that the dynamics of H and H-2 elimination from different sites are significantly di fferent. Relative branching ratios of H and H-2 elimination processes from different sites have also been determined. (C) 2000 American Institute of P hysics. [S0021- 9606(00)00815-1].