EVIDENCE FOR ACCELERATION OF THE INTRAMOLECULAR RELAXATION OF HYDRIDE STRETCHES BY SOME TYPES OF INTERNAL ROTATION. XIAOLIANG WANG.

Author Institution: Department of Chemistry., University of Akron.Intramolecular vibrational relaxation (IVR) appears to be a universal property of polyatomic molecules at energies where the vibrational density of states is sufficiently high. Evidence will be presented to show (i) that the presence of certain types of internal rotation degrees of freedom shortens the IVR lifetimes of hydride stretches, and (ii) that the IVR lifetimes increase with the distance of the hydride chromophore from the bond about which the relevant internal rotation occurs. Internal rotation which gives rise to distinct conformers appears to accelerate IVR but the 3-fold symmetric internal rotation of the methyl group In I-butyne does not. IVR lifetimes of two different hydride chromophores have been estimated for each of three molecules, ppentyne, ethanol, and propargyl alcohol. The correlation of the IVR lifetimes with distance is evident within each of these three molecules and is supported by single data points for a variety of other molecules. There is an indication of secondary effects such as retardation of IVR by halogenation or by insertion of a heavy atom into the carbon backbone