Experimental Confirmation of the Ion Cluster BeH(H₂)⁺

Abstract

Easterfield and Linnett¹ recently predicted the occurrence of the beryllium-hydrogen ion cluster, BeH(H₂)⁺ with n=1, 2 and 3. Their calculations indicated that the cluster with n=1 (that is, BeH(H₂)⁺) would have a particularly stable structure, its dissociation into BeH⁺ + H₂ requiring an energy of 38.3 kcalories mol⁻¹. In the course of an FIM-atom probe² analysis of G. P. Zone formation in Cu-12.7 at. % Be, we obtained experimental confirmation of the existence of this molecular species. Fig. 1a shows the Be end of the time-of-flight mass spectrum obtained from the Cu-Be alloy field-evaporated at 30 K in the presence of ∼ 10⁻⁶ torr hydrogen. The time of flight of each particle striking the ion detector was individually recorded and, except for a negligible few, all originated from the specimen surface. More than 25% of the intercepted beryllium-containing particles evaporated with M/n = 12, corresponding to BeH(H₂)⁺. Most of the remainder were BeH⁺ ions which had been observed previously by Barofsky³ and Mueller and Krishnaswamy⁴. There was no observable incidence of BeH(H₂)₂⁺ (M/n = 14) and BeH(H₂)₃⁺ (M/n = 16) which have calculated dissociation energies of only 6.7 and 6.6 kcalories mol⁻¹, respectively.