Time scales and mechanisms of intramolecular energy redistribution

The frequency-resolved spectra of CF3H, methanol, CF2Cl2, ethanol, and 1-butyne reveal a wide range of timescales and a variety of mechanisms for intramolecular vibrational and rotational energy redistribution. The fastest timescale ( tau less than or equal to 100 fs) is the result of strong anharmonic or harmonic low-order resonances. The longest directly measurable timescale (10 ps < tau < 300 ps) is evidenced by the width of the narrowest features in the methanol overtone spectra and by the clump widths in the eigenstate-resolved spectra of the ethanol fundamentals. The latter spectra indicate the simultaneous action of anharmonic, z-type Coriolis, and x/y-type Coriolis mechanisms. There are even longer timescales that cannot be determined directly from the spectrum of a bright state but can be deduced by modelling the data. For example, random matrix simulations indicate that the time for the completion of K-relaxation in ethanol is on the order of a nanosecond.