MECHANISM OF THE UV-LASER-INDUCED DESORPTION OF CO FROM CR2O3(0001)

The UV-laser-induced desorption of CO from an epitaxially grown film o f Cr2O3(0001) is reported using a (1+1') REMPI (resonance enhanced mul tiphoton ionisation) detection technique via the B-1 Sigma(+) electron ic state for the desorbing molecules to obtain information on single r ovibrational states. The final state distributions at three different wavelengths (6.4, 5.0 and 3.5 eV) were almost identical showing bimoda l velocity flux distributions for v '' = 0 and monomodal distributions for v '' = 1. The desorption cross-sections varied between (5.1 +/- 1 ) x 10(-18) cm(2) at 3.5 eV and (3.5 +/- 1) x 10(-17) cm(2) at 6.4 eV. The overall behaviour indicates that the excitation mechanism is due to a primary electronic excitation step within the substrate. Possible mechanisms are discussed.