IS LOCALIZED COLLISION RESPONSIBLE FOR O-2 PHOTODESORPTION FROM AG(110)

O-2 adsorbs in the troughs on Ag(110) at 100 K as a dioxygen species w ith its internuclear axis oriented along the [1 (1) over bar 0] azimut h. Irradiation of this surface by 248 nm light leads to dissociation a nd molecular O-2 desorption. The photodesorption cross section decreas es dramatically with the decrease in O-2 coverage. Angle-resolved meas urement carried out in a plane containing the [1 (1) over bar 0] azimu th shows enhanced desorption flux at 45 degrees with respect to the su rface normal. These results provide evidence for a displacement mechan ism in which an energetic O atom resulting from photodissociation disp laces a neighboring O-2 within the restricted alignment. Both localize d collision, i.e., momentum transfer, and substrate-mediated electroni c effects may be involved.