Isomerization in Gold Clusters upon O2 Adsorption

A systematic investigation is performed on structural transformations in small neutral gold clusters (Au-3-Au-12) induced by O-2 adsorption, with the use of the fully automated reaction path search techniques, i.e., anharrnonic downward distortion following (APDF) and artificial force induced reaction (AFIR) methods, implemented in the global reaction route mapping (GRRM) program. For each size of Au cluster, the most stable structure, low-energy isomers, and a network of isomerization pathways are determined. The located Au-n-O-2 adsorption forms can be classified into two groups: eta(1)-AunO2, where only one oxygen atom is adsorbed on Au-n, and eta(2)=AunO2, where both oxygen atoms are adsorbed on Au-n in a hridged manner. These two adsorption forms can be transformed to eath other with a low barrier. The isornerization pathways of gold clusters upon O-2 adsorption are compared with those obtained for the pure gold cluSters Without O-2. It is demonstrated that O-2 adsorption promotes structural transformations in gold clusters considerably by lowering the isomerization battlers. The presence of the unpaired electron is a necessary condition for O-2 adsorption in the eta(1)-Au O-2 form, as well as the subsequent cluster isomerization and the O-O bond activation. These conclusions ate consistent with the recent experimental resits by Fielicke et al.