INTRAMOLECULAR VIBRATIONAL-ENERGY REDISTRIBUTION IN THE ACETYLENIC C-H AND HYDROXYL STRETCHES OF PROPYNOL

The high-resolution infrared spectra of the acetylenic C-H and O-H str etches of propynol have been measured using an electric-resonance opto thermal molecular beam spectrometer (EROS). Both spectra display exten sive fragmentation of the hydride-stretch oscillator strength characte ristic of the intramolecular vibrational energy redistribution (IVR) p rocess. The IVR Lifetime is strongly mode-specific. The IVR lifetime o f the acetylenic C-H stretch is approximately 400 ps, with a slight in crease in the Lifetime with increasing values of the K-a quantum numbe r. The lifetime of the O-H stretch is 60 ps and is independent of the rotational quantum numbers. The experimental upper limit for the anhar monic state densities are 30 and 40 states/cm(-1) for the acetylenic C -H and O-H stretches, respectively. These values are in good agreement with the values obtained by a direct state count (19 and 32 states/cm (-1), respectively). The measured density of states increases with an approximate (2J + 1)-dependence. These results indicate that all energ etically accessible states are involved in the IVR dynamics. However, neither the acetylenic C-H nor the O-H stretch shows a decrease in Lif etime as the total angular momentum (J) increases. This result shows t hat Coriolis coupling of these two hydride stretches to the near-reson ant bath states is much weaker than the anharmonic coupling. For the O -H stretch, we are able to obtain the root-mean-squared (rms) matrix e lement for the Coriolis coupling prefactor, 0.0015(5) cm(-1). The rms anharmonic coupling matrix element is 0.03 cm(-1). For the low J value s measured in the O-H spectrum, the Coriolis-induced NR rate is much s lower than the initial redistribution rate resulting from the stronger anharmonic interactions leading to an IVR process with two distinct t ime scales. (C) 1998 American Institute of Physics.