Direct measurement of photoisomerization lifetimes for laser-excited methylcycloheptatriene molecules

Methylcycloheptatriene is irradiated by 15 ns flashes from a frequency-quadrupled Nd–YAG laser at 265 nm. The excited molecules undergo rapid internal conversion to vibrationally excited electronic ground state molecules. The lifetime for photoisomerization of these state-selected species under collision-free conditions is measured via light absorption of the hot species and/or the hot products. The nature of these spectra is discussed. The lifetimes are compared with calculations based on thermal isomerization experiments.