Experimental investigation of small He clusters, ch. 5

The intensities of the helium ions Hesub(n)+, n=1 to 4, have been measured as a function of the pressure P0 in the source of a molecular beam machine at 7K. Together with scattering experiments performed using an argon-filled chamber at 80K the measurements showed the He+ ions to be due to unclustered He atoms and the He2+ ions to originate from He3 clusters for P0 between 200 and 500 torr. The results are consistent with the prediction that He2 has no bound state. The heaviest ion detected was He13+ (at P0=1500 torr). (J.A.R.)