EXPERIMENTAL AND THEORETICAL STUDIES OF ETHYL

Abstract

First detected in 1988, the $-CH_{2}$ wagging fundamental of $C_{2}H_{5}$ recorded at high resolution by diode laser absorption extends from approximately 470 to more than $600 cm^{-1}$. The mode corresponds to the out-of-plane motion at the radical center and this is strongly coupled to the torsion or internal rotation in this species. We $published^{a}$ a preliminary analysis of the spectrum in 1996, but at the time recognized many questions remained. Aided by extensive ab initio calculations and the $detection^{b}$ of part of the spectrum at $3\mu m$ in a jet-cooled sample, we have recently made much progress understanding the details of the $20\mu m$ spectrum and the internal dynamics in the radical. In total, close to 500 transitions have been assigned in 18 rotation-torsion branches. The observation of branches involving levels with $m_{torsion} = 3$ and low $k_{a}$, in particular, has allowed much more precise estimates of the barrier to internal rotation and its change on vibrational excitation. Calculations of the torsion/wag potential surface have allowed a physical interpretation of these experimental results. Acknowledgement: This work was carried out at Brookhaven National Laboratory under contract DE-AC02-98CH10886 with the U. S. Department of Energy and supported by its Division of Chemical Sciences, Office of Basic Energy Sciences.