Knowledge Bank

The pure rotational infrared spectrum of a mixture of $H216O,H217O$, and $H218O$ 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 $50cm-1-730$ $cm-1$ was recorded in three parts using beam splitters $12\mu$ m, $5\mu$ m, and 2.5 $\mu m$ in thickness. The abundances of $H216O,H217O$, and $H218O$ 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 $H216O$ were compared with frequencies calculated from rotational energy levels given in the literature. The measured line positions of $H217O$ and $H218O$ were compared with values calculated from the rotation and distortion constants given in the literature. In the case of $H217O$, and $H218O$ we found differences greater than $1cm-1$ between the observed and calculated wavenumbers. New rotation and distortion constants, and rotational energy levels for $H217O$, and $H218O$ were calculated from the Observed frequencies.