Isomerization in Gold Clusters upon O₂ Adsorption

Abstract

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., anharmonic downward distortion following (ADDF) 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: η 1 -Au n O 2, where only one oxygen atom is adsorbed on Au n, and η 2 -Au n O 2, where both oxygen atoms are adsorbed on Au n in a bridged manner. These two adsorption forms can be transformed to each other with a low barrier. The isomerization 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 barriers. The presence of the unpaired electron is a necessary condition for O 2 adsorption in the η 1 -Au n O 2 form, as well as the subsequent cluster isomerization and the O–O bond activation. These conclusions are consistent with the recent experimental results by Fielicke et al.