ON THE NATURE OF HIGH $CH_{4}$ VIBRATIONAL LEVELS EXCITED BY PROTON ENERGY LOSS SPECTROSCOPY
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Date
1986
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Ohio State University
Abstract
The forced harmonic oscillator model, which has been applied to proton energy loss spectroscopy (PELS), is extended here to probe the nature of $CH_{4}$ vibrational levels excited by the proton beam. At each overtone of the triply degenerate $\nu_{3}$ vibration, there is a collection of vibrational sublevels which differ in the way amplitude is distributed of these sublevels with a propensity for the highest energy, most delocalized vibrations in each overtone band. Comparison is made with infrared multiphoton absorption which excites delocalized vibrations in $SF_{6}$ and with single photon overtone absorption which selects the most localized states. Peak positions in a simulated spectrum match the experiment up to $8\nu_{3}$ but for higher overtones the anharmonic shift is up to 0.05 eV less than observed. A demanding test of the model must wait for higher resolution experiments and better spectroscopic constants. It is suggested that high resolution PELS spectra could provide spectroscopic information not accessible by other methods.
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Address of Levene: Department of Chemistry, University of California, Irvine, CA 92717 Address of Perry: Department of Chemistry, University of Rochester, Rochester, NY 14627
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