ELUCIDATING THE DYNAMICS OF ACETYLECE IN THE $7000 CM ^{-1}$ ENERGY REGION
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Date
1992
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
In low resolution ($30 cm^{-1}$) Dispersed Fluorescence (DF) spectra of acetylene from $2v_{3}^{\prime}$ and $3v_{3}^{\prime}$ levels of $\bar{A}$ $A_{u}$, the expected Franck-Condon (FC) bright states are progressions in $v_{2}^{\prime\prime}$ (``CC stretch) and $V_{4}^{\prime\prime}$ (Irans-bend). It was hypothesized that two additional progressions prominent in the DF spectrum were either built on excited $v_{1}$ (sym, ``CH"""" stretch)$^{1}$, possibly FC bright due to the slight elongation of the CH bond in the A state, or on even quanta of $v_{5}^{\prime\prime}$ $(cis-bend)^{2}$ appearing via a strong but previously undetected $\DeltaV_{4}^{\prime\prime} = V_{5}^{\prime\prime}= \pm2$ Darling-Dennison (DD) resonance. Either assignment was plausible because $V_{1}^{\prime\prime}V_{2}^{\prime\prime}+2v_{5}^{\prime}$ In high resolution ($0.1 cm^{-l}$) Stimulated Emission Pumping (SEP) spectra of acetylene from the 2$v_{3}$^{\prime} level of the $\tilde{A}$ state to the $7000 cm^{-1}$ region of the $\tilde{X}$ state, the observation of two more $t=2$ levels than $t=0$ levels proves that not only is the DD assignment correct but, a well characterized $\DeltaV_{3}^{\prime\prime}$ (antisym ``CH” stretch)=-$\Delta v_{2}-\Delta v_{4}^{\prime\prime}=-Av_{5}^{\prime\prime}\pm1$ Fermi $resonance^{3}$ hasáallowed ($\nu_{1}, \nu_{2}, \nu_{3}, \nu_{4}, \nu_{5})=(0,0,1,5,1)$ to borrow intensity from (0,1,0,6,2) which in turn borrowed its intensity from the FC bright (0,1,0,8,0).""
Description
$^{1}$ E. Abramson, et. al., J. Chem. Phys., 83, 453 (1985). $^{2}$ K. Yamanouchi, et. al., J. Chem. Phys. 95, 6330 (1991). $^{3}$ B.C. Smith and J.S. Winn, J. Chem. Phys. 94, 4120 (1991).
Author Institution: Department of Chemistry, George R. Harrison Spectroscopy Laboratory; Department of Chemistry and George R.Harrison Spectroscopy Laboratory, Massachusetts Institute of Technology; Department of Pure and Applied Sciences, The University of Tokyo
Author Institution: Department of Chemistry, George R. Harrison Spectroscopy Laboratory; Department of Chemistry and George R.Harrison Spectroscopy Laboratory, Massachusetts Institute of Technology; Department of Pure and Applied Sciences, The University of Tokyo