Autoionization from High-Lying3p (P122)5np′Levels in Argon

A beam containing argon metastable atoms is crossed by the output beam of a pulsed tunable uv laser. The resulting ion production is measured as a function of wavelength within the range $2945<\mathrm{}\lambda <3075\mathrm{}$ Å and displays several sharp resonances. These arise from excitation of $\mathrm{Ar}\left({}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}\right)$ metastable atoms to high-lying $3p {}_{}{}^5{}_{}{}^{}\left({}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\right)n{p}^{\prime }$ levels which subsequently undergo autoionization. The term values of these levels are measured to an accuracy of ± 6 ${\mathrm{cm}}^{-1\mathrm{}}$ and are in excellent agreement with values obtained from a quantum-defect extrapolation of the known lower terms of this series. An unambiguous assignment of principal quantum numbers to the observed levels is therefore possible. The lifetimes against autoionization of these levels are longer than 2 ± ${10}^{-12\mathrm{}}$ sec.