Chemisorption and dissociation of single oxygen molecules on Ag(110)

The chemisorption of single oxygen molecules on Ag(110) and the dissociation of the adsorbed molecules induced by tunneling electrons were studied at 13 K using a variable-low-temperature scanning tunneling microscope. Two predominant types of chemisorbed O2 molecules were identified, one with the O2 molecular axis aligned along the [001] direction of the substrate [O2 (001)], and the other with the molecular axis aligned along the [1 1- 0] direction [O2 (1 1- 0)]. Tunneling of electrons between the scanning tunneling microscope tip and O2 (001) caused the molecule either to rotate or dissociate, depending on the direction of electron tunneling. In contrast, electron tunneling caused O2 (1 1- 0) to dissociate regardless of tunneling direction. In addition to O2 (001) and O2 (1 1- 0), several other oxygen species and their dynamical behaviors were observed.