Relative cross sections for electron-impact ionization of the rare-gas Van der Waals dimers ${\mathrm{Ar}}_2$, ArKr, ${\mathrm{Kr}}_2$, KrXe, and ${\mathrm{Xe}}_2$ have been measured with a mass spectrometer in the electron energy range from threshold to 180 eV. The following appearance potentials for direct ionization from the corresponding neutral dimers have been found: ${\mathrm{Ar}}_2^{+}$: 15.2±0.2 eV, Ar${\mathrm{Kr}}^{+}$: 14.0±0.2 eV, ${\mathrm{Kr}}_2^{+}$: 13.45±0.3 eV, Kr${\mathrm{Xe}}^{+}$: 12.2±0.2 eV, and ${\mathrm{Xe}}_2^{+}$: 11.75±0.3 eV. These values agree with those obtained in recent photoelectron studies. The appearance potential of ${\mathrm{Ar}}_2^{+}$ formation via associative ionization of argon atoms is found to be 14.6±0.2 eV.

• Received 4 December 1978

DOI:https://doi.org/10.1103/PhysRevA.19.2154