SUBMILLIMETER-WAVE SPECTROSCOPY OF SHORT-LIVED SPECIES USING A BOW

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1998

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Ohio State University

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A submillimeter-wave spectrometer using a BWO (Backward Wave Oscillator) has been constructed and applied to measurements for short-lived species. Thw BWO frequency was stabilized by a phase-lock loop, using a Schottky-type harmonic mixer which mixes the radiation from the BWO with that of a millimeter-wave $synthesizer^{1}$. A part of submillimeter power was reflected by a wire-grid beam-splitter and directed to the absorption cell. The transmitted power was detected by a magnetically-tuned, liquid-helium-cooled InSb bolometer. To test performances of the spectrometer, the rotational spectra of $NH_{2}OH, NH_{2}$ and CF have been measured in 400-500 and 600-800 GHz region. The $NH_{2}$ radical is known to be an important intermediate in astrochemistry and various chemical reaction process. The submillimeter-wave absorption spectrum was observed toward the dust continuum source Sagittarius $B2^{2}$. Recently, Tonooka et al. have measured the microwave spectrum and determined precise molecular $constants^{3}. NH_{2}OH$ has been interested because of its large amplitude internal motions. The submillimter-wave rotational spectra in the ground and vibrationally excited OH-torsion state have been observed for the first time. The accuracy of submillimeter-wave line positions of the CF-radical reported previously using a far-infrared laser side-band spectrometer is not enough to perform astronomical searches for this radical. In the present study the submillimeter-wave spectra of CF have been measured with same precision as microwave spectroscopy.

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$^{a}$ Domestic Research Fellow of Japan Science and Technology Corporation. $^{1}$ G. Winnewisser, Vib. Spectrosc., 8, 241 (1995); I. Morino et al. J. Mol. Spectrosc., 185. 142 (1997). $^{2}$ E.F. van Dishoeck et al., Astrophys. J., 416, L83 (1993). $^{3}$ M. Tonooka et al., J. Chem. Phys., 106, 2563 (1997).
Author Institution: National Institute for Advanced Interdisciplinary Research

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