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



S Davis, D Uy, David Nesbitt


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.
Journal of Chemical Physics
No. 4


infrared laser absorption, laser spectroscopy, stretch manifolds


Davis, S. , Uy, D. and Nesbitt, D. (2000), Laser Spectroscopy of Jet-Cooled Ethyl Radical: Infrared Studies in the CH<sub>2</sub> Stretch Manifold, Journal of Chemical Physics (Accessed December 4, 2023)
Created December 31, 1999, Updated October 12, 2021