No abstract

The collisional loss of vibrational energy from gas-phase toluene, pumped by a pulsed KrF laser operating at 248 nm, has been observed by monitoring the time-resolved infrared fluorescence from the C-H stretch modes near 3.3 p,m. The fragmentation quantum yield of toluene pumped at 248 nm was determined experimentally to be-6%. Energy transfer data were obtained for 20 collider gases, including unexcited toluene, and analyzed by an improved inversion technique that converts the fluorescence intensity to the bulk average energy, from which is extracted «!:..E», the bulk average amount of energy transferred per collision. Comparisons are presented of these results with similar studies of benzene and azulene, and with the time-resolved ultraviolet absorption study of toluene carried out by Hippler et al. [J.

Low pressure (53 μ) infrared multiple photon decomposition of several hydrocarbons requiring large fluences to produce measurable decomposition was investigated. Cyclopropane, propylene, methylcyclopropane, cis- and trans-2-butene, vinylcyclopropane, cyclopentene and 1-methylcyclopentene exhibit wide variations in reaction product yield and the spectral dependence of yield at constant pressure and fluence. The role vibrational state density, torsional vibrations and low intensity absorption cross section play in determining yields was examined. The results show the complex interplay of factors affecting multiple photon decomposition. Although the maximum observed yields tend to increase with increasing vibrational state density and absorption cross section, they were poorly correlated with either state density or cross section. The dependence of yield upon excitation wavenumber revealed several unexpected features which indicate that low energy vibrational level structure must be the dominant factor in determining yields. Also, the data suggest that torsional vibrations can ease the excitation bottleneck.