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Electron capture by protons in the tail of the electron density at a metal surface is investigated. The ion velocity is assumed to be large compared to the velocity of an electron in the lowest orbit of hydrogen. Electron transition probabilities into the 2p states of hydrogen are calculated, analogous to the first Born approximation by extending a model of Trubnikov and Yavlinskii [1] to tilted foils and nonzero angular momentum of the captured electron. From the density matrix the Stokes parameters are calculated. The results give partial agreement with experimental data, especially for the sinusoidal dependence of circular polarization on foil tilt angle.

Within a semiclassical approximation the excited-state density matrix is calculated for a resonant l s ~2p transition in a hydrogen-like projectile. The resonant coherent excitation process is induced by the periodic surface potential seen by the particle during its surface passage at grazing incidence. We find an anisotropic magnetic sublevel population which yields a high degree of polarization in a subsequent photon emission. The dependence of the Stokes parameters on both the relative orientation between the beam velocity v and the crystal axes and the surface potential decaying along the surface-normal are studied.

We present the first numerical results of a multichannel theory for resonant charge exchange in ionsurface scattering at grazing incidence. The time-dependent Schrodinger equation describing resonant exchange can be solved in the adiabatic approximation for the slow perpendicular motion. As an initial application the state dependence of the distance of formation in the H(« SB *2) following specular reflection of protons at a gold surface is determined. PACS numbers: 34.50.Fa, 34.50.Pi, 34.70.+e, 79.20.Rf Charge-exchange processes in ion-surface scattering at small grazing angles (0:<5 O ) provide the unique opportunity to study collision processes under unusual conditions not easily accessible by other means: Projectile ions reflected specularly at clean surfaces undergo an array of extremely soft collisions at the surface layer with distances of closest approach selected by the normal component of the projectile velocity. An even more interesting feature is that the electron capture from the conduction band of the metal into atomic orbitals is simultaneously characterized by two different time (or velocity) scales: a fast motion of the projectile (i?j|^u F ) in the surface plane and the near-adiabatic motion along the surface normal (v ± <^v^) where the characteristic internal velocity of the target electrons is the Fermi velocity vp. Both low-and high-energy methods therefore must be combined to describe inelastic electronic processes near the surface at intermediate velocities.The technique of ion-surface scattering at grazing incidence has recently been used in a large number of investigations in a broad range of different subfields such as the polarization characteristics of excited atomic manifolds, 1 " 3 the production of nuclear spin polarization, 4 surface channeling, 5 and the diagnostics of surface magnetic order. 6 For the understanding of the production mechanism of excited states itself as well as its application as a potential tool of surface diagnostics, detailed knowledge of the distance dependence of the formation process is required.As a first application of a new multichannel treatment of resonant charge transfer we calculate the formation distance from the surface of all substates H(/i~2,/m) following p -* Au collisions at intermediate projectile speeds (i? = l a.u.). The quantization axis is chosen to coincide with the surface normal. The gold surface is described by a (nearly) free-electron jellium model. The motion of the proton can be quite accurately approxi-mated by a classical trajectory since the de Broglie wavelength A, d is small compared to characteristic distances in the target or projectile. In the following we will be concerned only with the outward portion of the trajectory of the receding ion which is taken as a straight line. Deviations near the turning point as well as the inward portion are irrelevant for the formation of excited states for reasons to be discussed below. The electron transfer from a conduction-band state 0* to an atomic orbital j is then governed by a...

From a theoretical analysis we predict large fractions of circular polarization of light emitted by ions scattered from surfaces of ferromagnetic single crystals. Maximum enhancement of circular polarization as compared to surface ion scattering from non-magnetic materials is again expected at grazing incidence. A circular polarization of 89 % was estimated for the case of Ar § ions scattered from the (110) plane of a Ni single crystal.