Adsorption and Photochemistry of CF2Br2 (Halon 1202) on Highly Ordered Pyrolytic Graphite (HOPG)

Desorption of physisorbed molecular oxygen from coronene films and graphite surfaces

We present a study on the adsorption and desorption of molecular oxygen (O2) on highly oriented pyrolytic graphite (HOPG) and on coronene films deposited on it. To this end, DFT calculations were performed and experiments were made using the FORMOLISM device, which combines ultra-high vacuum, cryogenics, atomic or molecular beam and mass spectrometry techniques. We first studied the desorption kinetics of dioxygen (O2) on a coronene film and on graphite at 15K, using the TPD (Themally Programmed Desorption) technique. We observed that the desorption of O2 occurs at a lower temperature on coronene than on graphite. We deduce the binding energies which are 12.5 kJ/mol on graphite and 10.6 kJ/mol on coronene films (preexponentiel factor of 6.88x10^14 s^-1) . The graphite surfaces partially covered with coronene show both adsorption energies. These results are in good agreement with theoretical calculations, using as surfaces graphene and coronene adsorbed on graphene. It appears that O2 is better bound parallel to the surface and has a preference for the inner sites of the coronene