DIODE LASER SPECTROSCOPY OF THE $\nu_{2}$ BAND OF $CH_{2}$
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Date
1986
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Ohio State University
Abstract
The $\nu_{2}$ (bending) fundamental of $CH_{2}$ in its ground $^{3}B_{1}$ state was first studied1 using the laser magnetic resonance technique; 10 different rotation-vibration transitions were detected. Later a tunable diode laser was used$^{2}$ to observe $\nu_{2}$ in $CD_{2}$ and one further transition in $CH_{2}$. We have now greatly extended the study of $CH_{2}$ by measuring 53 new transitions in the $\nu_{2}$ band in the regions 800 to 911 and 1030 to $1173 cm^{-1}$. We use a diode laser spectrometer, Zeeman modulation, and a multiple reflection cell as in the earlier work,$^{2}$ but find somewhat different optimum conditions for $CH_{2}$ production, namely a mild discharge through a flowing mixture of ketene (=0.2 torr) and helium (=2 torr). Discharge modulation was also used to detect the $CH_{2}$ absorption, but the sensitivity was worse than for Zeeman modulation, partly because the $CH_{2}$ exhibited a surprisingly long lifetime ($=$1 ms) following the cutoff of the discharge. The new transitions extend to higher values of N (10) and $K_{a}$ (3) than were observed previously. Most important are 10 P- and Q-branch transitions of the $K_{a} = 2 + 3$ sub-band, since neither $K_{a}{^{\prime\prime}}=3$ nor $K_{a}{^{\prime\prime}}=2$ had been observed previously. A combined analysis of the available$^{1,2,3}$ data results in improved $CH_{2}$ parameters, notably for the spin-rotation interaction constant $c_{aa}$.
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$^{1}$ T.J. Sears, P.R. Bunker, and A.R.W. McKellar, J. Chem. Phys. 77, 5363 (1982). $^{2}$ A.R.W. McKellar, C. Yamada, and E. Hirota, J. Chem. Phys. 79, 1220 (1983). $^{3}$ T.J. Sears, P.R. Bunker, A.R.W. McKellar, K.M. Evenson, D.A. Jennings, and J.M. Brown, J. Chem. Phys. 77, 5348 (1982). Address of Marshall and McKellar: Herzberg Institute of Astrophysics, National Research Council of Canada, Ottawa, Ontario, Canada KlA OR6.
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