Electron impact excitation cross sections of helium atom levels from the 23S1 metastable state according to experiment and theory

The formation of triplet helium atom levels excited by electron impact from the 2(3)S(1) metastable state was studied and the corresponding cross sections were determined. The earlier suggested method for generalizing experimental and theoretical results is discussed and used. The method includes interpolation over the whole set of cross section values for each of the helium levels under study measured in our works and by other authors with a four-parameter approximation of the dependence of cross sections on the energy of incident electrons. The approximation parameters and the cross sections of 19 S, P, and D triplet levels of the HeI series with n = 2-10 calculated with the use of these parameters from the theoretical and experimental data are reported. Possible reasons for discrepancies between the experimental and theoretical cross sections, which differ by a factor of 1.5-2, are analyzed. Serial trends in electronic excitation cross sections from the 2(3)S(1) metastable state to the S, P, and D levels are studied. The fulfillment of the similarity relation for the Q(E) curves and the Bethe approximation for cross sections in the 2(3)S-n(3)P series are checked. It is shown that the suggested procedure for experimental and theoretical data processing allows errors of different methods to be taken into account and the accuracy and reliability of the final cumulative result to be increased.