THE $rQ_{K_{A}}$ BRANCHES $(K_{A} \in \{2,3,4\})$ OF CARBODIMIDE, HNCNH

Abstract

The $^{r}_{Q}{K_{A}}$ branches ($K_{A} \in{2,3,4}$) of carbodiimide, HNCNH, have been recorded with the tunable far infrared spectrometer available at the European Laboratory for Nonlinear Spectroscopy (LENS)$^{a}$. The main purpose of our measuring campaign at LENS was to record rotationally spectrum of the low-lying ($\approx 2.4$ THz) bending vibration $\nu_{7}$ of tricarbon oxide sulfide, $OC_{3}S$. This work was presented at the Thirteenth Colloquium on High Resolution Molecular Spectroscopy at $Riccione^{b}$. We used the strong {Q}-branch transitions of HNCNH to tune the spectrometer in order to observe the very weak transitions of the $\nu_{y}$-band system of $OC_{3}S$. The spectra obtained by this procedure contain new information on HNCNH. HNCNH, which exists in equilibrium with cyanamide in the vapour phase is a skew-chain molecule and by accident a nearly perfect symmetric top with $K = -0.999 995 368(18)^{c}$. The $^{r}_{Q}{K_{A}}$ branches which occur at approximately 1.8 THz, 2.5 THz and 3.2 THz, respectively, could be recorded rotationally resolved. A torsional doublet splitting was observed in all Q-branches. In addition asymmetry splitting could be detected within the $^{r}Q_{2}$ branch for $J > 18$. The spectra and the analysis will be presented.