Laser Spectroscopy of Jet-Cooled Ethyl Radical: Infrared Studies in the CH2 Stretch Manifold

Published

January 1, 2000

Author(s)

S Davis, D Uy, David Nesbitt

Abstract

A glow discharge, slit supersonic expansion in conjunction with direct infrared laser absorption methods has been utilized to record high resolution vibration-rotation spectra of the CH₃-CH₂ ethyl radical. The slit supersonic expansion results in efficient rotational cooling from discharge temperatures down to T _rotnearly equal to}14 K, permitting unambiguos rotational assignment and spectralanalysis for the first time. Furthermore, a discharge on/discharge off data collection scheme permitsclean discrimination between spectral contributions from radical vs precursor absorption. Spectra for both symmetric and asymmetric CH₂ stretch manifolds are observed. Least-squares fits of transition frequencies out of the K=O ground state manifold to a near prolate top model Hamiltonian reproduce the data to within the 7 MHz experimental uncertainty and provides rotational constants for both ground and vibrationally excited symmetric/asymmetric CH₂ stretchstates. The band origins for the CH₂ stretch vibrations [3037.01896(12) cm^-1 and 3128.69369(13)cm^-1] are in reasonable agreement with ab initio theory: though predictions for relative intensities of the two bands are off by nearly an order of magnitude and indicate that the transition moment vector is tiled 33 away from each C-H bond toward the C-C bond axis. Structural analysis based on the measured B and C rotational constants imply a C-C bond distance of 1.49 . This is consistent with partial (nearly equal to}15%) double bond character for the ethyl racical carbon frame and in excellent agreement with theoretical predictions.

Citation

Journal of Chemical Physics

Volume

112

Issue

No. 4

Pub Type

Journals

Keywords

infrared laser absorption, laser spectroscopy, stretch manifolds

Citation

Davis, S. , Uy, D. and Nesbitt, D. (2000), Laser Spectroscopy of Jet-Cooled Ethyl Radical: Infrared Studies in the CH₂ Stretch Manifold, Journal of Chemical Physics (Accessed December 14, 2024)