Excited-state potentials in the Na–Hg system: Analysis of rainbow scattering and polarization effects

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Abstract
In the region from 0.7 to 2.9 eV center‐of‐mass energy the total differential cross section for the scattering of laser excited sodium in its 3 2P3/2 state against ground state mercury has been measured. Characteristic features of this cross section are two well‐separated and undisturbed rainbow structures. Assigning these patterns to rainbow scattering from the Σ and Π branch, respectively, of the excited state potential and analyzing the experimental data in the elastic approximation, yields potential parameters for both branches. As available pseudopotentials for the Na–Hg system fail to reproduce our results, a Lennard‐Jones 8,6 model was assumed. Then the well depth and equilibrium distance for the Σ and Π potential are extracted as εΣ = 0.264 eV, εΠ = 0.755 eV and RΣ = 3.72 Å, RΠ = 3.46 Å. The observed variation of the rainbow amplitudes with the angle between the field vector of the linearly polarized light and the relative velocity of the collision pair is interpreted on the basis of the elastic approximation in correlation with the initial alignment of the sodium atoms induced by the laser excitation.