FREQUENCY-RESOLVED MEASUREMENT OF FAST INTRAMOLECULAR VIBRATIONAL-ENERGY REDISTRIBUTION (IVR) IN THE O-H STRETCH OF GAS-PHASE ETHANOL

The frequency-resolved, molecular-beam spectrum of the O-H stretch of ethanol near 3678 cm-1 has been measured at 10 MHz resolution using an electric-resonance optothermal spectrometer (EROS). A portion of the R branch of the predominantly a-type O-H stretch for the more stable trans conformer has been rotationally assigned using a high-sensitivity infrared-microwave double-resonance technique. The spectrum shows extensive near-resonant perturbations that characterize the intramolecular vibrational energy redistribution (IVR) process. Single rovibrational transitions of the O-H stretch normal mode are found to be fractionated into more than 60 transitions due to the coupling of the O-H stretch to the background of nearby vibrational states. The overall width of the collection of molecular eigenstates coming from a single zeroth-order rovibrational state in the vibrationally excited state gives a 25 ps lifetime for energy redistribution from the O-H stretch in trans-ethanol. This lifetime is in reasonable agreement with previous time-resolved measurements of the O-H stretch lifetime of 70 ps for ethanol in CCl4. Comparison of the two measurement techniques is discussed.