The adsorption and photochemistry of dibromodifluoromethane (Halon 1202) adsorbed on highly ordered pyrolytic graphite (HOPG) was studied using temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). Dibromodifluoromethane adsorbs molecularly at 85 K and the first layer saturates at a fractional coverage of 0.14 +/- 0.01 monolayer (ML). Molecular desorption occurs at similar to 140 K (monolayer) and similar to 110 K (multilayers) with desorption energies of 43.8 +/- 3.6 and 22.4 +/- 1.9 kJ/mol, respectively. Ultraviolet irradiation of the monolayer by a filtered Hg-arc lamp (225-350 nm) resulted in the formation of CF2Br and Br (major products) and Br-2 and C2F4Br2 (minor products). The estimated integrated dissociation cross-section was 1.9 x 10(-19) cm(2) close to the calculated value for CF2Br2(g) ( 1.5 x 10(-19) cm(2)). The similarity of these two values implies that photodissociation of CF2Br2(ad)/HOPG is dominated by direct photoabsorption of the adsorbate and not electronic processes moderated by the substrate. The influence of the surface is most clearly observed in the distribution of products measured by TPD. We attribute the differences observed between adsorbate and gas phase/matrix isolation experiments to the high density of photogenerated species trapped in the surface layer.