Torsional Tunneling andA1–A2Splittings and Air Broadening of therQ0andpQ3Subbranches of the ν7Band of Ethane
✍ Scribed by A.S. Pine; S.C. Stone
- Publisher
- Elsevier Science
- Year
- 1996
- Tongue
- English
- Weight
- 259 KB
- Volume
- 175
- Category
- Article
- ISSN
- 0022-2852
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✦ Synopsis
The strong and sharp r Q 0 and p Q 3 subbranches of the n 7 perpendicular band of C 2 H 6 near 3000 cm 01 are located in atmospheric windows and have been observed in several remote monitoring measurements of ethane using infrared solar absorption spectroscopy. We report here difference-frequency laser measurements of the air broadening and shifting of these Q branches at T Å 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 with broadening coefficients of Ç0.67 cm 01 /MPa at 296 K and temperature exponents (g ϰ T 0n ) of n Ç 1. The peculiar Doppler contours of these Q branches are unresolved, even at the lower temperatures. Therefore, in order to model their blended contours, we have recorded their sub-Doppler fine structure using a color-center laser optothermal molecular beam spectrometer. We have resolved torsional tunneling splittings in both Q subbranches and anomalous A 1 -A 2 splittings in p Q 3 with the individual J components exhibiting distinctive nuclear-spin weights. 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.