Knowledge Bank

A $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi -2\Sigma$ band of gas phase $C2H$ centered at 2928 $cm-1$ is observed using a high resolution difference-frequency laser spectrometer. The $C2H$ molecules were produced in a hollow cathode discharge in a mixture of $C2H2$ ($\sim 15$ m Torr), $H2(\sim 0-150mTorr)$, and He $(\sim 700mTorr)$. Measurements were carried out using discharge modulation method at 3 kHz with a current of about 800 mA. Total laser pathlength was 36 m in a White cell arrangement. We have tentatively assigned this band to be the $3\nu 2+\nu 3$ combination band of $C2H$. In addition, two $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi -2\Pi$ transitions of $C2H$ connecting known states were also recorded. The common lower level of the two bands is the $X~(010)$ state, with the upper levels being the same as those of the known 3693 and $3600cm-1$ bands, respectively.