Knowledge Bank

The emission spectrum of the argon dimer has been studied in the VUV region. Liquid nitrogen cooled argon was excited with a rf (Tesla coil) discharge. A 6.65-m McPherson vacuum spectrograph equipped with a platinum-coated 2400 lines/mm ruled grating is used and provides a reciprocal dispersion of 0.3 {\AA}/mm in the second order. Only the band system $I(1)$ appeared with discrete structure. The rotational analysis of the bands indicates that the coupling scheme in the lowest excited state is closer to Hund-Mulliken case b than to case c, so that the excited symmetry may be assigned approximately as $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma u+$ rather than $1u,Ou-$. An attempt has been made to use spectroscopic results to depict the shapes and positions of the long-range portions of the first two excited states ($\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma u+$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma u+$) of $Ar2$ relative to each other and to the ground state $X1\Sigma g+$.