Knowledge Bank

Two-step excitations in MgO have been observed by use of an $Ar+$ laser (4765, 4965 and 5145 {\AA} lines) and a tunable dye laser (5660 $\cong$ 6250 {\AA}), The initial B-X excitations by the $Ar+$ laser have been discussed in the preceding paper- Further excitations by the dye laser at selected frequencies were detected through fluorescences in the UV range. The excitation spectra and the UV fluorescence spectra from each individual double resonance confirm the symmetries of the upper states. Four pairs of transitions (P and R) to the $E1\Sigma +$ state and six groups of transitions (PQR) to new $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi$ state(s) were observed. The analysis is in progress to determine the spectroscopic constants of the $E1\Pi$ state for which one E-X band has recently been rotationally analysed by Singh. The analysis of the new $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Pi$ state(s) is also in progress.