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.
