Spontaneous Deprotonation of HO₂^• at Air–Water Interface

HO₂^• is a crucial radical in atmospheric chemistry, with applications ranging from HO₂^•/OH^• interconversion to controlling the budget of various trace gases in the atmosphere. It is known that one of the potential sinks for HO₂^• is clouds and aerosols, though the mechanism is not clear to date. In the present study, using Born-Oppenheimer molecular dynamics simulations, we have demonstrated that the dissociation of HO₂^• on the surface of a water droplet, as well as in the bulk phase, is a spontaneous process. In addition, we have computed the Gibbs free energy for the deprotonation of HO₂^• on both the surface and in the bulk, which suggests that deprotonation of HO₂^• on the surface occurs faster compared to the same in the bulk.