HIGHER J- AND K-TRANSITIONS IN THE INFRARED SPECTRUM OF THE CO-Ar COMPLEX
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Date
1993
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Ohio State University
Abstract
A recent $analysis^{I}$ of the spectrum of CO-Ar in the $4.7 \mu m$ region was based on two complementary techniques: (1) a pulsed slit-jet supersonic source used with a tunable diode laser spectrometer, and (2) a long-path low-temperature static absorption cell used with a Bomem Fourier transform spectrometer. We have now extended this study by using a different combination of resources, namely the long-path cell with a diode laser spectrometer. This gives higher resolution and sensitivity than the FT spectrometer, and higher temperatures (and thus J- and K-values) than the supersonic jet. We used a diode laser manufactured by M\""{u}tek, mounted in a conventional Laser Analytics cold head. The laser beam made 32 traversals of a 5.5 m cell, for a total path of 176 m at a temperature of 77 K. The total gas pressure was about 1 torr, with a Ar:CO ratio of about 10:I. The CO-Ar absorption was detected by frequency modulation of the diode followed by phase-sensitive demodulation of the transmitted signal at 2f. Wave number calibration was made by means of simultaneous recording of signals from an absorption cell containing $N_{2}O$ and a temperature-stabilized solid Ge etalon The new data enable some significant extensions to be made in the assignments of the spectrum; for example, in the $K_{a} = 2 \leftarrow 1$ subband, the maximum J-value is raised from 19 to 28 in the Q-branch, and from 21 to 27 in the R-branch. Furthermore, the original analysis involved subbands with Ka-values of 3 or less, and we now find some evidence (also present in the FT spectra) for subbands with $K_{a} = 6 \leftarrow 5, 5 \leftarrow 4$, and $4 \leftarrow 3$. But there appear to be some perturbations which make it difficult to be absolutely certain about these assignments.
Description
$^{1}$. A.R.W. McKellar, Y.P Zeng, S.W. Sharpe, C. Wittig, and R.A. Beaudet, J. Mol. Spectrosc. 153, 475 (1992).
Author Institution: Herzberg Institute of Astrophysics, National Research Council of Canada
Author Institution: Herzberg Institute of Astrophysics, National Research Council of Canada