Cross sections and threshold effects for electron-impact excitation of the (2s$sup 2$) $sup 1$S and (2s2p) $sup 3$P states of helium
The energy and intensity of scattered electrons resulting from excitation of the (2s$sup 2$) $sup 1$S and (2s2p) $sup 3$P autoionizing states of helium have been measured as a function of incident electron energy. For incident energies only slightly higher than the threshold for (2s$sup 2$) $sup 1$S excitation, post-collision interactions between the scattered and ejected electrons cause the slowly moving scattered electron to lose an amount of energy proportional to E$sup -1$$.$$sup 25$/sub ex/ (where E/sub ex/ is the energy the scattered electron would have had in the absence of a post-collision interaction). This energy dependence compares well with an energy gain of the ejected electron proportional to E$sup -1$$.$$sup 2$/sub ex/, obtained by previous workers. Measurements of the intensity of scattered electrons show that both $sup 1$S and $sup 3$P total cross sections peak at threshold and have magnitudes about (2.0 and 4.0) x 10$sup -20$ cm$sup 2$, respectively, then rise to broad maxima of magnitudes about (2.5 and 5) x 10$sup -20$ cm$sup 2$ about 4.0 eV above their thresholds. A subsidiary peak at 59.0 eV in the $sup 3$P cross section is attributed to decay of the previously unidentified (2s2p$sup 2$) $sup 2$S He$sup -$ state into the $sup 3$P channel. The magnitude, energy, and width of this resonant structure in the $sup 3$P channel agrees with theoretical predictions. (AIP)
- Research Organization:
- Argonne National Laboratory, Argonne, Illinois 60439
- NSA Number:
- NSA-33-015679
- OSTI ID:
- 4084204
- Journal Information:
- Phys. Rev., A, v. 12, no. 6, pp. 2353-2360, Other Information: Orig. Receipt Date: 30-JUN-76
- Country of Publication:
- United States
- Language:
- English
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