A combined experimental and theoretical investigation of photodissociation dynamics of IBr− and IBr−(CO2) on the B (${}^2\Sigma _{1/2}^ +$Σ1/2+2) excited electronic state is presented. Time-resolved photoelectron spectroscopy reveals that in bare IBr− prompt dissociation forms exclusively I* + Br−. Compared to earlier dissociation studies of IBr− excited to the A′ (2Π1/2) state, the signal rise is delayed by 200 ± 20 fs. In the case of IBr−(CO2), the product distribution shows the existence of a second major (∼40%) dissociation pathway, Br* + I−. In contrast to the primary product channel, the signal rise associated with this pathway shows only a 50 ± 20 fs delay. The altered product branching ratio indicates that the presence of one solvent-like CO2 molecule dramatically affects the electronic structure of the dissociating IBr−. We explore the origins of this phenomenon with classical trajectories, quantum wave packet studies, and MR-SO-CISD calculations of the six lowest-energy electronic states of IBr− and 36 lowest-energy states of IBr. We find that the CO2 molecule provides sufficient solvation energy to bring the initially excited state close in energy to a lower-lying state. The splitting between these states and the time at which the crossing takes place depend on the location of the solvating CO2 molecule.