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2014 On présente ici une recherche semi-empirique des potentiels du dimère Ne*2, pour les états se dissociant en Ne(3P0,2) + Ne(1S0). Partant des potentiels ab initio calculés par Cohen et Schneider, on a déterminé une modification 2014 aussi faible que possible et restreinte au seul domaine des distances intermédiaires (4-10 u.a.) 2014 conduisant à un accord amélioré de la théorie et des expériences effectuées aux énergies thermiques. La modification proposée n'affecte que l'état 303A3u+. Il en résulte, après diagonalisation de l'interaction spin-orbite, des diminutions homógènes des potentiels 0-u , 1u(3P2) et 0-u(3P0). La bosse présente sur les deux premiers se trouve ainsi abaissée (de 108 à 21 meV), ce qui donne un accord satisfaisant avec les expériences effectuées sur la collision Ne(3P2)-Ne(1S0), particulièrement pour ce qui est de l'effet arc-en-ciel. L'élargissement imposé au puits 1u se trouve confirmé par le spectre d'émission de l'excimère. Aux énergies inférieures à 80 meV, la collision Ne(3P0)-Ne(1S0) est considérée comme purement élastique. Aux énergies supérieures, l'intervention de couplages dynamiques provoque une perturbation de la section efficace élastique, et l'apparition du processus superélastique: 3P0~1,2. On interprète ces deux effets en utilisant un modèle à deux états. Abstract. 2014 A semi-quantal interpretation of the Ne*2 potentials, for states dissociating into Ne(2p5 3s, 3P0,2) + Ne(2p6, 1S0) is presented. Starting from the ab initio potentials calculated by Cohen and Schneider, one determines a modification 2014 as small as possible and confined to the intermediate distance range (4-10 a.u.) 2014 yielding a better agreement between theory and experiment in the thermal energy range. The proposed modification affects only the 303A3+u state. After the diagonalization of the spin-orbit interaction, it results in consistent diminutions of the 0-u-1u(3P2) and 0-u(3P0) potentials. The hump of the two former states is lowered (21 meV instead of 108 meV) which gives good agreement with experiments on the Ne(3P2)-Ne(1S0) collision, especially for the resulting rainbow effect. The widening imposed on the 1u-well is confirmed by the excimer emission spectra. At energies below 80 meV, the Ne(3P0) + Ne(1S0) collision is considered as purely elastic. Above this energy, dynamical couplings induce a perturbation of the elastic differential cross section and the 3P0~1,2 superelastic process. These latter effects are interpreted by using a simplified 2-state model.

High-frequency Floquet theory (HFFT) is again applied to photoionization in a linearly polarized field of the hydrogen atom in its ground state. The new feature is the systematic use of a two-pole approximation to represent both the dressed potential (with two positive charges) and the coupling responsible for one-photon ionization (with two charges of opposite sign). Within such a scheme, both the initial bound and the final continuum states can be very accurately determined. The final continuum state is obtained by deriving, from Floquet theory, an equation involving a source term. The model accounts reasonably well, even at rather low frequencies, for the stabilization of the atom in an intense field and supports the claim that HFFT represents the photoionization rate with a golden rule expression involving dressed states.

A fully quantal close-coupling treatment of the excitation of helium on the levels 23S, 21S and 23P in the He+ on He collision. In addition to the lower Sigma g state, described at any distance by the configuration 1s sigma g(2p sigma u)2, eight simple configurations of symmetry Sigma g are introduced. After the 9*9 configuration interaction they combine into eight molecular states which dissociate into specific atomic states. The main interactions with the entrance channel consist of two localised couplings at two crossing points (R=1.34 au and 1.48 au). A two-state approximation is valid to interpret the 23S excitation. The results are in good agreement with the experimental data.