Rare gas collisional perturbation of the (6 3D1, 6 1D2) levels of mercury : a theoretical estimate

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Abstract
A theoretical model is developed, accounting for the effects (relaxation and transfer of tensorial quantities) of rare gas collisions with mercury atoms in either of two very close (δE ≃ 3 cm-1) levels 6 1D2 and 6 3D1. Two types of effective potentials are used : Van der Waal's Veff 1 = C6 R-6 and Veff 2 = C6 R-6+C8 R-8 which includes the two first non zero terms in the long range atom-atom interaction development. One gets a much better agreement between observed and calculated transfer or relaxation cross-sections using Veff 2 rather than the Van der Waal's potential (no parameter has been adjusted in either case). The only failure of Veff 2 calculations bears on orientation transfer cross-sections; it suggests that close range collisions play a more significant role in this process than assumed here. Calculations were performed for several temperatures in the 295-900 K range; the predicted thermal variation laws will be subsequently tested against the results of experiments currently in progress