Knowledge Bank

Li-Ar molecules have been produced in a supersonic beam by expanding a mixture of Ar gas and Li vapor through a nozzle into a vacuum. A temperature of about $800\circ C$ is required in the stagnation area in order to get a sufficient amount of Li atoms in the gas phase. The high-resolution absorption spectrum of the $A2\Pi \leftarrow X2\Sigma$ transition of LiAr has been measured between 14720 and 14895 $cm-1$ by scanning a cw dye laser and by observing the laser-induced fluorescence light. Rovibrational quantum numbers could successfully be assigned to about 750 molecular absorption lines of the isotopomer $\mathrm{<mrow\; data-mjx-texclass="ORD">7</mrow>}$LiAr and to about 120 lines of $\mathrm{<mrow\; data-mjx-texclass="ORD">6</mrow>}$LiAr. The parameters of molecular rotation, of spin-orbit interaction and of $\lambda$-type doubling have, up to now, been obtained for vibrational levels $v\prime \prime =0\dots 2$ of $X\Sigma$ and for $v\prime =5\dots 8$ of $A\Pi$. The molecular spin-orbit interaction of the $A\Pi$ state is about 10 times larger than the spin-orbit splitting of the $2 2P$ state of the Li atom. Preliminary values of equilibrium distance and well-depth are: 4.87(1) {\AA}, $41(2)cm-1$ for $X\Sigma$ and 2.49(5) {\AA}, $900(80)cm-1$ for $A\Pi$.