  We apply Kramers theory to investigate the dissociation of multiple bonds
under mechanical force and interpret experimental results for the
unfolding/refolding force distributions of an RNA hairpin pulled at different
loading rates using laser tweezers. We identify two different kinetic regimes
depending on the range of forces explored during the unfolding and refolding
process. The present approach extends the range of validity of the two-states
approximation by providing a theoretical framework to reconstruct free-energy
landscapes and identify force-induced structural changes in molecular
transition states using single molecule pulling experiments. The method should
be applicable to RNA hairpins with multiple kinetic barriers.
