ROTATIONAL ALIGNMENT IN THE UV-LASER INDUCED DESORPTION OF CO FROM CR2O3(0001)

The rotational alignment of the laser-induced non-thermal desorption o f CO adsorbed on an epitaxially grown film of Cr2O3(0001) has been stu died using 193 nm (6.4 eV) laser light and a (1 + 1')-REMPI technique. At low rotational quantum numbers J the molecules desorb like a 'heli copter' (J-vector perpendicular to the surface) while at high J-values a 'cartwheel' like motion is preferred (J-vector parallel to the surf ace). CO is adsorbed in a flat geometry as a single species. The resul ting angular momentum alignment in the laser desorption is interpreted qualitatively as a sum of effects due to corrugation of the surface i n the initial state and a change of the adsorption geometry in the int ermediate state before desorption.