Knowledge Bank

The branches ($KA\in 2,3,4$) of carbodiimide, HNCNH, have been recorded with the tunable far infrared spectrometer available at the European Laboratory for Nonlinear Spectroscopy (LENS). 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, $OC3S$. This work was presented at the Thirteenth Colloquium on High Resolution Molecular Spectroscopy at $Riccioneb$. 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 $OC3S$. 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 $K=-0.999995368(18)c$. The 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 branch for $J>18$. The spectra and the analysis will be presented.