Metal atoms as superbases: the gas phase proton affinity of uranium

The determination of the proton affinity of the uranium atom, measured as PA(U) = 238 +- 4 kcal/mol, led to the conclusion that metal atoms can be very strong bases in the gas phase. The endothermic reactions of uranium ion with D2 and CD4 were observed in an ion beam collision chamber and the threshold values for the interactions were determined. It is suggested that the high proton affinity of uranium is a result of a low ionization potential and a moderately high homolytic bond dissociation energy