Plasmon coupling to core hole excitations in carbon

The results from soft X-ray appearance potential spectroscopy (SXAPS), photon-induced Auger appearance spectroscopy h(cross) omega -APS), X-ray photoelectron spectroscopy (XPS) and ionization loss investigations on the carbon K level in graphite are compared. It is shown that plasmon excitation accompanies core hole creation and that the coupling in XPS is much smaller than in SXAPS, in sharp contrast to the situation pertaining in the simple metals. Plasmon coupling probably takes place in the case of h(cross) omega -APS and of ionization loss, but it is difficult to assess its magnitude. The transition probabilities for the various experiments are calculated within the framework of a simple model. The coupling constants for core and conduction electrons are different in graphite, leading to the observed anomalous behaviour.