Photodissociation dynamics of propene at 157.6 nm: Kinetic energy distributions and branching ratios

Abstract

Photodissociation dynamics of propene at 157.6 nm has been investigated in a molecular beam apparatus using the photofragment translational spectroscopic technique combined with the vacuum ultraviolet ionization method. Eleven photofragments have been successfully detected and ascribed to eight (five binary and three triple) dissociation channels: namely, C3H5+H, C3H4+H+H, C3H4+H2, C3H3+H2+H, C2H4+CH2, C2H3+CH3, C2H2+CH4, and C2H2+CH3+H. Their branching ratios have been determined to be 1%, 7%, <0.2%, 17%, 6%, 4%, 5%, and 60%, respectively. The complicated multichannel dissociation process has a propensity towards triple dissociations, notably the C2H2+CH3+H channel. In addition, the averaged kinetic energy releases and the fractions in translational energy have also been determined from the measured kinetic energy distributions. For the binary dissociation channels, the fractions in translational energy are less than 18% except the C3H5+H channel, whereas they are more than 42% for the triple dissociation channels. An intriguing finding indicates that the C2H4+CH2 channel has a nearly identical kinetic energy distribution and a similar branching ratio to the C2H3+CH3 channel, although the former undergoes a three-center elimination process different from the C–C bond rupture occurring in the latter.