Hornbeck—Molnar Cross Sections for the n=3 States of Helium

Analysis of the atomic light originating from energy levels of principal quantum number n=3 in the helium positive column shows that a pressure‐dependent loss process exists for states other than the S states. The loss mechanism is identified as the Hornbeck—Molnar process, $${\mathrm{He}}^{*}+\mathrm{He}\to {\mathrm{He}}_2^{+}+{\mathrm{e}}^{-},$$ by observing the effects of varying the atomic populations when the positive column is irradiated with intense atomic light. Comparison of the pressure‐dependent loss rate with the radiation loss rate from a particular state yields the Hornbeck—Molnar cross section. An independent measurement relating the molecular‐ion concentration to the 3³D population yields a separate value for the 3³D cross section, which agrees quite well with that measured by the previous method.