COMPETING MECHANISMS FOR INTRAMOLECULAR VIBRATIONAL REDISTRIBUTION INTHE NU(14) ASYMMETRIC METHYL STRETCH BAND OF TRANS-ETHANOL

The extensively perturbed spectrum of the asymmetric methyl stretching vibration of trans-ethanol near 2990 cm-1 has been reinvestigated via direct absorption infrared spectroscopy at a resolution of 30 MHz. A ground state combination difference analysis of the vibrational state mixing is presented for the upper state levels K(a)' = 0-2 and J' = 0- 4. The analysis indicates that the rotationless 0(00) level is anharmo nically coupled to the dark bath states. The effective number of pertu rbing states in each rovibrational transition increases with both J an d K(a) providing evidence for rotational involvement in intramolecular vibrational redistribution (IVR). The decrease of the average dilutio n factor from phi(d) = 0.41 at K(a)' = 0 to phi(d) = 0.09 at K(a)' = 2 and the increase of the average interaction width from DELTAepsilon = 0.04 cm-1 at K(a)' = 0 to DELTAepsilon = 0.19 cm-1 at K(a)' = 2 indic ate an a-type Coriolis component to the bright-bath coupling. In the K (a)' = 0 series the dilution factor decreases rapidly from phi(d) = 0. 92 at J'= 0 to phi(d) = 0.14 at J' = 3 indicating that b,c-type Coriol is coupling also plays a significant role in the IVR process. The effe ctive level density rho(eff)c for all of the observed transitions lie above the total vibrational state density rho(vib) = 9 levels per cm-1 and most are closer to the total rovibrational state density rho(rovi b) = (2J+1) rho(vib). This suggests that following a coherent preparat ion of the asymmetric methyl stretching vibration, the ensuing dynamic s explores all of the energetically accessible vibrational phase space of both the gauche and trans forms and much of the accessible rovibra tional phase space, i.e., that the K(a) quantum number is at least par tially destroyed. The C-H stretch is deduced to decay with a 59 ps IVR lifetime to the asymptotic probability of 0.24.