Isothermal desorption of O2 from Ag(001)

The relevant parameters which characterise molecular desorption of O-2-Ag(001) have been determined under isothermal conditions in the low coverage limit, using the beam-Bag method. We find a desorption order n=1.07+/-0.10, a desorption energy E-des=0.50+/-0.12 eV and a pre-exponential factor v(des)1013.3+/-3.5 S-1. Such values compare well with the thermal desorption parameters present in literature for molecular oxygen adsorbed on Ag(110). The much lower dissociative adsorption probability of O-2 on Ag(001) is therefore due to the existence of a different dissociation mechanism and not to a difference in the desorption probability compared with Ag(110).