Photoionization studies of the diatomic heteronuclear rare gas molecules XeKr, XeAr, and KrAr

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The photoionization efficiency curves of the heteronuclear rare gas van der Waals molecules XeKr, XeAr, and KrAr were obtained with the molecular beam technique in the wavelength range from 790 to 1065 Å (11.64–15.69 eV). The ionization potentials were found to be 11.757±0.017 eV for XeKr, 11.985±0.017 eV for XeAr, and 13.425±0.020 eV for KrAr. From the known dissociation energies of the ground state XeKr, XeAr, and KrAr van der Waals molecules as determined by low energy molecular beam elastic scattering experiments, the binding energies for the ground state of the heteronuclear rare gas molecular ions were deduced to be 0.37±0.02 eV for XeKr+, 0.14±0.02 eV for XeAr+, and 0.59±0.02 eV for KrAr+. The photoion spectra of the heteronuclear rare gas dimers R1R2 exhibit prominent autoionization structure, which is found to correlate very well with the excited molecular Rydberg states R1*R2 and R1R2* formed by the interaction of a normal ground state rare gas atom R1 (or R2) and an excited atom R2* (or R1*), in the n′p5(2P1/2,3/2) ns (nd) configuration (where n′=3 for Ar, n′=4 for Kr, and n′=5 for Xe). The excitation of XeKr, XeAr, and KrAr is found to obey the parity selection rule Δl=±1, in agreement with previous experimental observations in the photoionization studies of Kr2 and Ar2. The Rydberg series 5p2(2P1/2) ns (nd) for Xe, and 4p5(2P1/2) ns (nd) for Kr, which is manifested as autoionization lines in the photoion spectra of the van der Waals rare gas dimers XeAr and XeKr, respectively, were red shifted with respect to the positions in the photoionization efficiency curves of Xe and Kr. This allows one to calculate the potential energy for the excited molecular Rydberg state at a distance which corresponds to the equilibrium interatomic distance of the ground state van der Waals molecule. For Xe[5p5(2P1/2) ns (nd)]+Ar(1S0) one obtains 0.06 eV and for Xe(1S0)+Kr[4p5(2P1/2) ns (nd)] 0.10 eV. These values are found to be in agreement with what one would expect from a charge induced-dipole interaction.