Knowledge Bank

A millimeter-wave spectrometer equipped with a free space cell and on-line computer averaging has been employed to measure the absorption spectrum of HCNO in the frequency range 60--400 GHz. This covers the rotational transitions between J=2$\rightarrow$3 and $J=17\to 18$. For each rotational transition observed up to $J=11\to 12$, at least 17 vibrational satellites have been assigned. All of the $l$-components of transitions in the following vibrational states have been observed: These transitions have been analyzed on the basis of the Nielsen-Amat formulation of the rotation-vibration interaction in linear molecules. The rotational constants B and D as well as the vibration-rotation constant $\gamma g\prime$ could be obtained from sum rules valid for each group of perturbed lines. The vibrational constants $g44$, $g55$, $g45$ and $r45$ could then be determined from least squares fitting of the transition frequencies. With the exception of the components of the 00002 level, all of the lines could be fit to within the experimental error. Most of the measurements were reproducible to within $\pm$ 5 kHz or less in the fundamental frequency of the klystron. Preliminary measurements of the Lamb dip of the ground state rotational transitions were also obtained.