Borovik O. Electron excitation of subvalence shells in alkali metal atoms

Using the electron spectroscopy method and the crossed electron-atom beam technique, the excitation dynamics of electron spectra in alkali metal atoms was investigated in the impact energy region from the excitation thresholds up to 600 eV. The spectroscopic classification of the lines was performed by involving theoretical calculations of excitation energies, cross-sections, and decay rates for 1sn1l1n2l2 states in Li atoms and nр5n1l1n2l2 states in Na (n=2), K (n=3), Rb (n=4), and Cs (n=5) atoms. Autoionizing states in molecules Li2, Na2, Rb2 were revealed. The absolute values of the effective excitation cross-sections for the atomic and molecular autoionizing states were obtained. The near-threshold excitation of the subvalence shells is exclusively of a resonance character due to the formation of short-living states (resonances) of negative ions. The excitation energies, spectroscopic classification and decay channels for such states were determined. The effect of the post-collision interaction was investigated; in particular, in the ejected-electron spectra of Na and K atoms a new behaviour was discovered - a negative energy shift of the (np5[n+1]s2) 2P3/2,1/2 lines under a resonance excitation of the corresponding levels. A qualitative model of the effect for the alkali metal atoms was proposed. The absolute values of the autoionization cross-sections were obtained for all alkali atoms. The maximal relative contribution of autoionization to the total single ionization cross-section by electron impact was estimated to be 2, 5, 26, 32, and 39% for Li, Na, K, Rb and Cs atoms, respectively.