PURE ROTATIONAL SPECTRA OF $H_{2}^{17}O$ AND $H_{2}^{18}O$ BETWEEN $50 CM^{-1}$ AND $730 CM^{-1}$

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The pure rotational infrared spectrum of a mixture of $H_{2}^{16}O, H_{2}^{17}O$, and $H_{2}^{18}O$ was measured with a resolution of 0.010$cm^{-1}$. The spectrum was recorded on the Fourier transform spectrometer [1,2] constructed at the University of Oulu. The region $50 cm^{-1}-730$ $cm^{-1}$ was recorded in three parts using beam splitters $12\mu$ m, $5\mu$ m, and 2.5 $\mu m$ in thickness. The abundances of $H_{2}^{16}O, H_{2}^{17}O$, and $H_{2}^{18}O$ in the sample were about 47%, 24% 29% respectively. The accuracy of the observed line positions is better than 0.001$cm^{-1}$ for unblended lines. About 1100 lines were assigned in the spectrum. The measured frequencies of $H_{2}^{16}O$ were compared with frequencies calculated from rotational energy levels given in the literature. The measured line positions of $H_{2}^{17}O$ and $H_{2}^{18}O$ were compared with values calculated from the rotation and distortion constants given in the literature. In the case of $H_{2}^{17}O$, and $H_{2}^{18}O$ we found differences greater than $1 cm^{-1}$ between the observed and calculated wavenumbers. New rotation and distortion constants, and rotational energy levels for $H_{2}^{17}O$, and $H_{2}^{18}O$ were calculated from the Observed frequencies.


$^{1}$J. Kauppinen, Acta Univ. Oul. A38 (1975); Appl. Opt. 14, 1987 (1975). $^{2}$J. Kauppinen, Appl. Opt. 18, 1788 (1979).
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