Ions and atoms in superfluid helium (⁴He). IV. Temperature dependence of the mobility of alkali earth ions

New experimental results for mobilities in superfluid helium of the alkali earth ions Be+, Mg+, Ca+, Sr+ and Ba+ in the temperature region from 1.27 up to 1.66 K are reported. Surprisingly, the temperature dependence of the Be+ ion mobility, measured here for the first time, is more similar to that of the He+ ion than to the heavier alkali earth ions. This behavior may suggest a snowball like structure for the defect around Be+ in contrast to the bubble like defects around the heavier alkali earth ions. © Springer-Verlag 1997.