Intramolecular vibrational energy transfer in methyl formate

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Intramolecular vibrational energy transfer in isolated gas phase molecules of methyl formate has been studied by spectrally resolving the IR laser induced fluorescence from C–H stretch fundamentals, combination bands, and overtones in the region from 2900 to 3500 cm−1. By comparing the experimentally observed relative energy content of the IR active modes with that calculated from a statistical model it is concluded that complete randomization of the energy initially deposited in the zeroth order optically excited state occurs. However, due to the finite density of vibrations, that statistical distribution differs clearly from a thermal distribution. Both the model and experiment agree that different optically excited states deposit different amounts of energy in the carbonyl stretching mode at 1754 cm−1. We also observe a rotational state dependence of vibrational energy transfer in the 2939 cm−1 band. The experiments are performed by exciting a molecule cooled in a nozzle expansion with light from an infrared optical parametric oscillator. The fluorescence spectra are recorded with a cryogenic Michelson interferometer.