SYMMETRY AND SPECTROSCOPIC CONSTANTS OF THE UPPER STATE OF THE VACUUM UV EMISSION CONTINUUM OF $Ar_{2}$

The red-degraded first continuum of $Ar_{2}$, which begins at 1074 {\\AA} $^{1}$ (the energy of the $^{3}P_{2}$ metastable) shows oscillatory structure out to 1500 {\\AA}. A semiclassical $procedure^{2}$ has been used to derive the upper state potential curve between 2.0 and 3.2 {\\AA} from the observed structure and different assumed lower (repulsive) potentials. Vibrational levels were found numerically, and a comparison of computed level spacings with those observed by Tanaka and $Yoshino^{3}$ for the $1_{u}$ state (dissociation limit $^{3}P_{2} + ^{1}S_{0}$) and the $0^{+}_{u}$ state (limit $^{3}P_{1} + ^{1}S_{0}$) show that the radiating state is a high vibrational level ($v^{\\prime} = 22 \\pm 2)$ of $O^{+}_{u}$ rather than a continuum level of $1_{u}$. Spectroscopic constants for $O^{+}_{u}$ depend somewhat on the assumed lower potential; we obtain $D^{\\prime}_{e} = 6000 \\pm 500$ $cm^{-1}$, $\\omega^{\\prime}_{e} = 310 \\pm 30$ $cm^{-1}$, $\\omega_{e}x^{\\prime}_{e} = 2.5 \\pm 0.5$ $cm^{-1}$, and $R^{\\prime}_{e} = 2.32 \\pm 0.1$ {\\AA}. These constant agree well with those predicted by assuming that $O^{+}_{u}$ is a Rydberg state with configuration $Ar_{2}$ ($X ^{2}\\Sigma^{+}_{u}$) $4s\\sigma_{g}$. Calculations of bound-continuum emission from low vibrational levels of $O^{+}_{u}$ confirm that it is also the upper state of the second continuum of $Ar_{2}$ which peaks at $\\sim$ 1270 {\\AA}.