Role of autoionization in the near-threshold photoionization of argon and krypton metastable atoms

A molecular-beams apparatus is used in conjunction with a pulsed tunable uv laser to study the photoionization of argon and krypton $m{p}^5\left({}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\right) \mathrm{}(m+1\mathrm{})\mathrm{}{s}^{\prime }:\left({}_{}{}^3{}_{}{}^{}P_0^{}{}_{}{}^{}\right)$ and $m{p}^5\left({}_{}{}^2{}_{}{}^{}P_{\frac{3}{2}}^{}{}_{}{}^{}\right) \mathrm{}(m+1\mathrm{})s:\left({}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}\right)$ metastable atoms in the wavelength range 3250-2690 Å. Major contributions to the ionization arise from excitation to $p^5\left({}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\right)n{f}^{\prime }$ and $p^5\left({}_{}{}^2{}_{}{}^{}P_{\frac{1}{2}}^{}{}_{}{}^{}\right)n{p}^{\prime }$ levels which autoionize into the underlying $P_{\frac{3}{2}}$ continuum. Term values are presented for these levels and compared with those calculated by extrapolation of the lower levels of these series, whose term values are known from spectroscopic observations. The widths of the autoionizing peaks are discussed together with the relative transition probabilities.