Ra. Bennett et al., MECHANISTIC STUDIES OF THE PHOTODISSOCIATION OF PHYSISORBED O-2 GRAPHITE/, Journal of physics. Condensed matter, 6(10), 1994, pp. 1955-1964
We have investigated the vacuum ultra-violet photodissociation of mole
cular O2 physisorbed on graphite using synchrotron radiation with phot
on energies in the range 13-35 eV. The yield of desorbed O+ ions shows
a threshold at approximately 19.5 eV and resonances at 24.5 eV and 28
.5 eV, contrasting strongly with the gas phase photodissociation cross
section. The principal mechanism of O+ production appears to be dipol
ar dissociation driven by photoelectrons generated in the substrate. A
n enhancement in the detection efficiency of low-energy ions, compared
with previous measurements, has identified an additional dissociation
mechanism leading to the desorption of O- ions. Specifically, the res
ults support a channel for low-energy O- desorption, attributed to the
dissociative attachment of photoelectrons, again generated in the gra
phite substrate, to the physisorbed O2 molecules.