van der Waals interactions between an atom and a planar surface exhibit a quadrupolar component in D(2)(z)-D(2)/3 (D, atomic dipole; ź, normal to surface). This coupling is responsible for an atom symmetry break, mixing levels of the same parity such as metastable 3P0, 3P2 levels of rare gas atoms. The strongly exoenergic 3P0-3P2 transition in Ar and Kr is observed by a time-of-flight technique, using as a surface the edge of a copper slit. The results confirm the predicted strong peaking of the angular distribution of inelastically scattered atoms and give a good estimate of the transition probability.
Surface-induced transitions between Zeeman sub-levels of metastable neon atoms traversing a micro-slit copper grating are investigated. The quadrupolar part of the surface van der Waals interaction suddenly perturbs the evolution of the Zeeman sub-levels in a magnetic field B , giving rise to van der Waals - Zeeman transitions. Exothermal inelastic transitions are identified by the related deflection γ. In a diagram (γ, B 1/2 ) the location of the inelastic peaks is fitted by straight lines of slopes proportional to |Δ m | −1/2 , where Δ m is the magnetic number change.
Summary form only given. Summary from only given. In the non retarded regime, atom-surface van der Waals (vW) interactions originate in the forces between the fluctuating atomic dipole and its instantaneous image linked to polarisation charges induced in the surface. vW interactions which are generally attractive (distance law in 1/z3) are of fundamental importance in many fields of physics. The existence of vW repulsion has recently been demonstrated when there is a resonant coupling between the fluctuating atom dipole and a surface resonance. We have started an experimental study of surface-induced wave function mixing between the 3P/sub 0/ and 3P/sub 1/ metastable states of argon. A thermal metastable argon beam is velocity selected thanks to a time of flight (TOF) technique.
Dans cette thèse, on a montré l'occurrence de transitions exothermiques et endothermiques entre les niveaux métastables 3P_2 et 3P_0 dans la collision d'atomes de gaz rare avec une surface solide. Le développement d'une source d'atomes métastables utilisant le processus d'échange de métastabilité au sein d'un jet supersonique a permis ensuite d'observer la diffraction par un réseau de nanofentes, puis, dans une expérience de collision sur un réseau micrométrique en Cuivre en présence d'un champ magnétique externe, d'observer des transitions Zeeman au sein du niveau 3P_2. Le calcul, à partir des données spectroscopiques, de l'interaction de van der Waals entre un atome d'argon métastable dans l'état 3P_2 et une surface conductrice plane a révélé outre une partie scalaire, une partie quadrupolaire modifiant l'énergie des sous niveaux au voisinage de la surface. Un modèle d'évolution soudaine prédit alors une probabilité de transition dont l'ordre de grandeur est en accord avec l'expérience.
Helium dimer in its metastable triplet electronic state, He
2(a 3Σu+), is a promising candidate for direct laser cooling and precision measurements. Interactions and collisions involving He
2(a 3Σu+) remain unexplored in ultracold and cold energy domains. Here, we present the first theoretical investigation of intermolecular interactions and collision dynamics of He
2(a 3Σu+)+Ne van der Waals complex. For the ground electronic state,
X 3A′, we employ a spin-restricted coupled cluster method with single, double, and noniterative triple excitations. The resulting interaction potential exhibits an extremely shallow well with a depth of 4.612 cm
−1. We construct a three-dimensional vibrationally averaged potential energy surface. Using this surface, we perform full close-coupling calculations including fine-structure levels of He
2(a 3Σu+) to investigate collisional excitation and quenching induced by Ne. We analyze the low-energy scattering dynamics and model resonant features associated with quasi-bound states supported by interaction potential. Propensity rule for fine-structure conserving transitions is established. We additionally consider He
2+Ar collisions and compare their energy dependence and resonance structure with those of He
2+Ne. The He
2+Ar system exhibits a richer resonance structure, highlighting the sensitivity of low-energy scattering to interaction potential and reduced mass. Calculated PES and scattering properties provide a reliable benchmark for description of He
2+Ne van der Waals complex and may be useful for interpretation of future experimental spectra and collision measurements.