COHERENCE-CONVERTED POPULATION TRANSFER FTMW-IR DOUBLE RESONANCE SPECTROSCOPY OF CH3OD IN THE C-H STRETCH REGION
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Date
2010
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Publisher
Ohio State University
Abstract
Coherence-converted population transfer microwave-infrared double resonance spectroscopy is employed to record the rotationally state-selected infrared spectra of jet-cooled CH$_3$OD in the C-H stretch region (2750$-$3020 cm$^{-1}$). The observed infrared spectra result from the E-species microwave transitions (1$_0$ \leftarrow 1$_{-1}$ at 18.957 GHz, 2$_0$ \leftarrow 2$_{-1}$ at 18.991 GHz, and 3$_0$ \leftarrow 3$_{-1}$ at 19.005 GHz). The present spectra of CH$_3$OD contain 17 interacting vibrational bands ($J^{\prime}$ = 0). In additional to the three C-H stretch fundamentals ($\nu_3$:2841.7 cm$^{-1}$, $\nu_9:2954.4 cm$^{-1}$ and $\nu_2:2998.9 cm$^{-1}$), 14 additional band origins are found in the region of the binary combinations of the CH bends (2890$-$2950 cm$^{-1}$). Although the A-species was inaccessible in the present work, the pattern of E-species reduced energies suggests that the torsional tunneling splittings of $\nu_3$ and $\nu_9$ are normal, whereas $\nu_2$ is inverted. The number and distribution of the observed vibrational bands support a stepwise coupling scheme in which the CH stretch bright state couples first to the binary C-H bend combinations, and then to all of the higher order vibrational combinations. A time-dependent interpretation in the asymmetric region indicates a fast (170 fs) initial decay of the bright state.
Description
Author Institution: Department of Chemistry, The University of Akron, Akron OH 44325; Department of Chemistry, University of Virginia, McCormick Rd., Charlottesville, VA 22904