TORSIONAL SPLITTING, K-DOUBLING AND AIR BROADENING OF THE $\nu_{7} {^{1}Q_{0}}$ AND $^{p}Q_{3}$ SUBBRANCHES IN ETHANE
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Date
1995
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Ohio State University
Abstract
The strong and sharp $Q_{0}$ and ${^{p}}Q_{3}$ subbranches of the $\nu_{2}$ perpendicular band of $C_{2}H_{6}$ near $3000 cm^{-1}$ are located in atmospheric windows and have been observed in numerous remote monitoring measurements of ethane using infrared solar absorption $spectroscopy^{1}$. We report here differnce-frequency laser measurements of the air broadening and shifting of these Q branches at T = 296 and 160 K in order to improve the quantitative analysis of the atmospheric spectra. The air-broadened spectra can be fit to high accuracy by convolving the Doppler-limited spectra with single shifted Lorentzians of $HWHM 0.671 (13) cm^{-1}/MPa at 296 K$ and $\gamma \propto T^{n}$ exponents n = 1.02(2). The peculiar Doppler contours of these Q branches are unresolved, even at low $temperatures^{2}$, so we have recorded their sub-Doppler molecular beam optothermal spectra to be able to model the blended contours. We have resolved torsional tunneling splittings and an anomalous $A_{1}-A_{2}-type$ K doubling in $^{p}Q_{3}$ with the individual J components exhibiting distinctive nuclear-spin $weights^{3}$. These splittings are induced by high-order torsional background perturbing states with localized irregularities making it difficult to model the spectra with simple J(J + 1) power series.
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1. C.P. Rinsland et al., JQSRT 52, 273 (1994); and references cited therein. 2. A.S. Pine and W.J. Lafferty, J. Res. NBS 87, 237 (1982). 3. E.B. Wilson, Jr., J. Chem. Phys. 6, 740 (1938); J.T. Hougen, J. Mol. spectrosc. 82, 92 (1980).
Author Institution: National Institute of Standards and Technology, Gaithersburg, MD 20899.
Author Institution: National Institute of Standards and Technology, Gaithersburg, MD 20899.