Knowledge Bank

The vacuum ultraviolet spectrum of the fourth positive $(A1\Pi -X1\Sigma +)$ system of $\mathrm{<mrow\; data-mjx-texclass="ORD">13</mrow>}C18O$ generated in emission in a jet discharge apparatus was photographed in the spectral region 1460-1670 {\AA} for the first time on a 10.6 m vacuum grating spectrograph. Detailed rotational analysis of nineteen bands involving seven vibrational levels ($v=0,1,2,4,6,7$, and 9) of the $A1\Pi$ state was carried out. Several perturbations occurring in the $A1\Pi$ state due to its neighbouring states $e3\Sigma ,a3\Sigma +,d3\Delta iI1\Sigma$ and $D1\Delta$ were observed. The 1-0 band of the intercombination system $e3\Sigma --X1\Sigma \prime$ was observed because of ``intensity borrowing” from the A-X system. From a deperturbation analysis, depertured molecular constants were obtained for the specified seven vibrational levels as well as for the perturbating states. Perturbation parameters and mixing coefficients which characterize the perturbations were also derived.