A time-of-flight technique is used for the measurement of positive ion mobilities in argon in the 1–100 atm pressure range at 300 °K. The ions are produced by photoionization of gas atoms in the drift region with ultraviolet light from a spark discharge.
A mobility is found which varies continuously with the reduced electric field
E/p
0 and which exhibits two saturation values at 1.55±0.01 cm
2/volt sec (for
E/p
0
2 volt/cm torr) and at 0.818±0.003 (for
E/p
0
0.17). The former value is in excellent agreement with the zero-field mobility obtained by Beaty for Ar
+. The last value is interpreted in terms of the Langevin theory and connected with the formation of the Ar
33
+
labile cluster. This has the Ar
+ ion as nucleus and is surrounded by two complete shells of 12 and 20 argon atoms respectively. A mean value of the cluster radius is estimated as 6.24 Å.
Den Herren Prof. Dr. W.Lochte-Holtgreven und Prof. Dr. J.Richter danken wir für ihr förderndes Interesse an dieser Arbeit sowie für wertvolle Ratschläge. Der Humboldt-Stiftung sei an dieser Stelle für die finanzielle Unterstützung ebenfalls gedankt.