It was proposed previously that Br-2-sensitized photolysis of liquid CO2 proceeds through a metastable primary photoproduct, CO2Br2. Possible mechanisms for such a photoreaction are explored here computationally. First, it is shown that the CO2Br radical is not stable in any geometry. This rules out a free-radical mechanism, for example, photochemical splitting of Br-2 followed by stepwise addition of Br atoms to CO2-which in turn accounts for the lack of previously observed Br-2+CO2 photochemistry in gas phases. A possible alternative mechanism in liquid phase is formation of a weakly bound CO2:Br-2 complex, followed by concerted photoaddition of Br-2. This hypothesis is suggested by the previously published spectroscopic detection of a binary CO2:Br-2 complex in the supersonically cooled gas phase. We compute a global binding-energy minimum of -6.2 kJ mol(-1) for such complexes, in a linear geometry. Two additional local minima were computed for perpendicular (C-2v) and nearly parallel asymmetric planar geometries, both with binding energies near -5.4 kJ mol(-1). In these two latter geometries, C-Br and O-Br bond distances are simultaneously in the range of 3.5-3.8 angstrom, that is, perhaps suitable for a concerted photoaddition under the temperature and pressure conditions where Br-2 + CO2 photochemistry has been observed.