Observation of Jet-cooled Radical and Ion by Millimeterwave Spectroscopy Combined with Pulsed-jet Expansion and Discharge Nozzle Technique.

Author Institution: Department of Chemistry Faculty of Science, Kyushu UniversityMillimeterwave spectrometer combined with a pulsed supersonic jet nozzlc and discharge nozzle was devised and applied to observe the absorption spectra of the jet-cooled radicals and ions in the 100-300 GHz region. Within a cylindrical electrode ($I = 300$, and $100 \phi$) as cathode, a pulse jet nozzle attached $1\phi$ tantalum (10 mm long) tube as anode was placed. Sample gas diluted in several atm of Ar to a few % was injected in the cell with repetition rate of 10 - 30 Hz synchronized with discharge pulse. Millimeterwave was focused tightly just below the nozzle by teflon lenses. So far we observed $J = 3 -2$ rotational lines of $CS (^{\Sigma^{+}})$ produced by the discharge of $CS_{2}$. The sensitivity of the spectrometer is estimated to be $\Delta I\Pi-3\times 10^{-6}$ from the signal to noise ratio of the $^{33}S$ isotopic species. We also observed the $N=1 - 0$ rotational line of the $CN (^{2}{\Sigma^{+}}$) radical, which was split into seven due to fine and hyperfine structures, with S/N ratio of about 30. The $J = 2 -1$ rotational line of the $DCO^{+}$ ion (${1^\Sigma}^{+}$) was observed with S/N ratio of about 3, The rotational temperature of molecules within discharge is estimated to be a few ten K. The application of this millimeterwave spectrometer for the detection of light unstable molecules, and for the detection of the van der Waals mode transitions of radical cluster is of great interest