Laboratory studies of helium ion loss processes of interest in the ionosphere

Preliminary measurements of reaction rates for loss of thermal helium ions in reaction with molecular oxygen and nitrogen establish rather conclusively that the helium ions in the ionosphere will be lost in reaction with molecular nitrogen rather than molecular oxygen in contrast to previous assumptions based on theoretical considerations. The rate of thermal He⁺ loss in reaction with N₂ is measured to be 1·2 ± 0·3 times the rate for reaction with O₂. This conclusion is of considerable significance to atmospheric physics because the oxygen loss process contained the possibility of leading to terrestrial helium escape and therefore the possibility of a steady state helium atmosphere. The nitrogen loss process does not have this possibility so that no satisfactory mechanism has yet been proposed which will allow a steady state helium atmosphere. The interpretation of recent atmospheric helium ion profiles obtained by rocket borne mass spectrometers appear to be inconsistent with the laboratory loss rate constants and current atmospheric theory.