Peculiarities in optical excitation functions of Zn and Cd atoms.

We report on the results of a thorough study of the excitation functions for the spectral lines of the Zn I (n=5-7) and Cd I (n=6,7) principal series. Experimental setup similar to that in [1] was used in the present study with electron beam energy spread of $\sim $0.7 eV. The measured excitation functions have a number of features (mostly maxima) in the autoionizing region which are similar for Zn and Cd but less clear in the Cd case. The first features (shoulders), located near the ionization threshold just below lowest nd$^{10}$np$^{2}$ autoionizing terms (n=4 for Zn, n=5 for Cd), could be the evidence of an effective Zn$^{-}$ (Cd$^{-})$ np$^{3}$ state formation. The most prominent features were observed at $\sim $12 eV and $\sim $16 eV in Zn and at $\sim $13 eV in Cd. They are located at the energies just above the parent terms 3d$^{9}$4s$^{2}$4p and 3d$^{9}$4s$^{2}$5p in Zn and 4d$^{9}$5s$^{2}$5p in Cd, with the specific energy shifts which can be attributed to the post-collision interaction population mechanism. [1] G. G. Bogachev and E. Yu. Remeta, Optics and Spectroscopy \textbf{86}, 647 (1999).