Features of the excitation of lines of the principal series of zinc-subgroup atoms by electron impact. I. Cadmium

Using the technique of crossed beams of slow electrons and cadmium atoms, the excitation functions of three spectral lines of its principal series (166.9, 152.7, 146.9 nm) outgoing from the $5snp^{1}P^\circ_{1}$ levels were measured ($n$ = 6, 7, 8, respectively). In the range of electron energies 12–18 eV, a manifestation of the post-collision interaction of slow scattered electrons and fast electrons ejected during the decay of autoionizing states was found in these functions. This process, at incident electron energies of $\sim$11.8, $\sim$12.4, and $\sim$16.6 eV, leads to additional population of the initial levels of spectral transitions and, correspondingly, to maxima on the excitation functions due to the capture of a scattered electron to these excited levels. The terms of autoionizing states of the atom responsible for the observed maxima on the excitation functions of spectral lines are established. In the classical approximation, by two methods – direct calculation and least squares approximation – estimate the effective widths of the electronic decay of autoionizing states, the combined action of which leads to an energy shift of the maxima. Approximate calculation formulas are used, which are valid for various relations between the post-collision shift of the maxima on the excitation functions and the binding energy of atomic levels.