Biological and Chemical Physics
Helium dimer ion was observed after electron impact ionization of a supersonic expansion of helium with translational temperature near 1 mK. The dependence of the ion signal on source pressure, distance from the source, and electron kinetic energy was measured. The signal was determined to arise from ionization of neutral helium dimer.
Luo, Fei; McBane, George C.; Kim, Geunsik; Giese, Clayton F.; and Gentry, W. Ronald, "The Weakest Bond: Experimental Observation of Helium Dimer" (1992). Peer Reviewed Articles. 6.