Elsevier

Chemical Physics

Volume 121, Issue 2, 1 April 1988, Pages 211-235
Chemical Physics

Long-range intermolecular potentials for the metastable rare gas-rare gas systems Ar*, Kr*(3P0,2)+Ar, Kr, Xe

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Abstract

In a crossed beam experiment with a calibrated supersonic secondary beam the absolute value (rms accuracy 2.5%) and the velocity dependence of the total cross section Q have been measured in a wide range of relative velocities 500<g<5000 m s−1 for the title systems. The data have been analysed with the ion-atom Morse-Morse-spline-van der Waals potential of Gregor and Siska for the Ne*-Xe system as a reference, resulting in accurate values for the well depth ϵ, well position Rm and long-range pure van der Waals constants C6 (without the influence of C8 and C10). These long-range pure C6 values are in excellent agreement with the calculated values of Dalgarno for the corresponding alkali atom-rare gas systems when scaled with the ratio of polarisabilities. The major difference in comparison with the alkali systems is the larger influence of the higher-order dispersion terms C8 and C10 (due to the (np)−1 core hole), as reflected in the velocity dependence of the attractive contribution Qa ∝ (2ϵRm/ħg)2/(s−1) with s=6.5–7 for high velocities and in the large amplitude of the glory contribution Qgl. For all systems the interesting N=1 glory maximum has been observed, with the glory range extending to the N=1.5 minimum for Ar*-Ar and to the N=6 maximum for Kr*-Xe. For the homonuclear systems only the glory oscillations due to the van der Waals-type potentials are observed. The glory damping due to the scattering on multiple potentials is described in terms of a rms spread Δ(ϵRm) in the ϵRm product, e.g., for Ar*-Ar we find Δ(ϵRm)/ϵRm=0.13. These measurements are fully complementary to the high-energy differential cross section measurements of Gillen et al., which only probe the chemical type potential with a deep well. For the heteronuclear Kr*-Xe system a strong velocity-dependent damping of the glory oscillations is observed, which can be described quantitatively by an excitation transfer process to a near-resonant short-lived Xe**((5p)5 (6p)) state. The characteristic velocity dependence is used to calculate the radial coupling matrix element for this transition.

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  • Cited by (0)

    1

    Present address: Chemistry Department, Princeton University, Princeton, NJ 08544, USA.

    2

    Present address: Shell Research BV, PO Box 60, 2280 AB Rijswijk, The Netherlands.

    3

    Present address: Hogeschool Eindhoven, Rachelsmolen 1, 5612 MA Eindhoven, The Netherlands.

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