The core hole clock method
Charge transfer times τCT at surfaces are often too short for conventional laser techniques which are limited to τCT > few fs.
Examples: Values of τCT for physisorbates and chemisorbates on transition metal surfaces:
Alternative technique: Use the well known lifetimes of a core hole (e.g. [N1s]: 6.4 fs) as an "internal clock" for the investigation of charge transfer dynamics.
Example: atom / molecule at a surface:
Resonantly excited electron may delocalize a) before or b) after core hole decay.
Result: Core decay spectrum with two different contributions: Normal Auger + Resonant Auger Raman fractions.
a) Resonantly excited electron still present:
Raman contribution; constant binding energy
b) Resonantly excited electron delocalised:
Normal Auger decay; constant kinetic energy
From ratio of the two contributions AND lifetime of core hole tcore:
Charge transfer time τCT !
fR: Contribution of the Auger Raman fraction from fit of data.
Note: Screening by electron transfer FROM the substrate contributes to the "normal" fraction