Comparisons of Infrared Multiple Photon Reaction Yields of Some C3–C6 Hydrocarbons

Abstract

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.