The transition path sampling technique was used to determine trajectories connecting the interface and bulk for the transfer of a hydroxyl radical from the air-water interface to the water bulk. The trajectories were used to calculate the rate of transfer for the process. In addition, transition state and Grote-Hynes theories were used to calculate the rate of transfer. It was found that transition state theory significantly overestimated the rate of transfer, while the Grote-Hynes theory estimated a transmission coefficient that was fairly close to that from transition path sampling. Analysis of transition states found that a majority of them were not at the free energy barrier from the potential of mean force, but shifted towards the vapor phase. (c) 2007 Elsevier B.V. All rights reserved.