Mixed-valence correlations in charge-transferring atom-surface   collisions
  Motivated by experimental evidence for a mixed-valence state to occur in the neutralization of strontium ions on gold surfaces we analyze this type of charge-transferring atom-surface collision from a many-body theoretical point of view using quantum-kinetic equations together with a pseudo-particle representation for the electronic configurations of the atomic projectile. Particular attention is paid to the temperature dependence of the neutralization probability which--experimentally--seems to signal mixed-valence-type correlations affecting the charge-transfer between the gold surface and the strontium projectile. We also investigate the neutralization of magnesium ions on a gold surface which shows no evidence for a mixed-valence state. Whereas for magnesium excellent agreement between theory and experiment could be obtained, for strontium we could not reproduce the experimental data. Our results indicate mixed-valence correlations to be in principle present, but for the model mimicking most closely the experimental situation they are not strong enough to affect the neutralization process quantitatively. 
M. Pamperin, F. X. Bronold, and H. Fehske
cond-mat.str-el