**
ELECTRON TRANSFER IN SLOW ATOM-SURFACE COLLISIONS:
A CLOSE-COUPLING APPROACH WITH CONTINUUM DISCRETIZATION
**

Bogdana Bahrim and Uwe Thumm

JRM Laboratory, Department of Physics, Kansas State University
Manhattan, Kansas, USA

Charge transfer during atom-metal surface collisions
has received much interest in the last decade. In
contrast to other close-coupling approaches^{1}, we
discretize the active electron's motion inside the metal
using Weyl wave packets^{2}. These stationary wave
packets have the advantage of being localized at the
surface, where the electronic interactions occur. The use
of discretized states to represent the conduction-band
continuum allows for the convenient inclusion of (one
electron) inelastic processes inside the substrate.

We solve the time-dependent Schrödinger equation
as a system of coupled differential equations for the
atomic and metallic population amplitudes, using a
two-center expansion for the total wavefunction of the
active electron^{3}. The "metallic part" of the total
wavefunction is discretized in momentum space in a finite
triple sum (corresponding to the Ox, Oy and Oz directions)
of Weyl wave packets. For the electron motion
along the normal to the surface, wave packets are obtained
by superimposing jellium wave functions within
a small interval δ_{z} about the centroid
momentum *k _{zi}*,

where the reflection and transmission coefficients, R and T, and the decay parameter γ are evaluated at the centroid momentum

The system of close-coupled equations is integrated
numerically. We have studied the evolution of the
atomic and metallic population amplitudes for a Hydrogen
atom at perpendicular incidence on an Aluminum surface
with speed v_{z}=0.02 a.u. Hybridization
effects have been investigated, indicating that a significant
part of the hybridization near a metal surface
corresponds to the "Stark-like" mixing of spherical hydrogenic
states in the non-uniform field of the surface.

Figure 1 shows the squared amplitudes in parabolic
representation of the *n* = 2, *k* = -1,+1 states, of
all *n* = 3 states, and of all 200 Weyl packets used
to discretize the conduction band continuum, as a
function of D-*d _{min}*. D is the atom-surface distance
and

We have also found that the atomic and metallic populations at the end of the collision are very sensitive to the screening of the interaction potential which couples the metal states.

**Figures:**

**References:**

1) P. Kiirpick, U. Thumm, and U. Wille, Phys. Rev. A 57, 1920 (1998)

2) G. Schiwietz, Phys. Rev. A 42, 296 (1990)

3) B. Bahrim. and U. Thumm, Surf. Sci. 451, 1 (2000)

This work was supported by the
Chemical Sciences, Geosciences and Biosciences Division,

Office of Basic Energy Sciences,
Office of Science,
U.S. Department of Energy.

*Submitted to ICPEAC 2001, July 2001 in Santa Fe, NM.*

*This abstract is also available in
Postscript or
Adobe Acrobat formats.*