When molecules meet: a femtosecond study of the protonation of a base

The femtosecond dynamics of bi-molecular reactions is difficult to study as a common starting point for the reacting molecules cannot be established. However, by photochemical conversion of an un-reactive molecule into a reactive molecule, we can effectively mix two equilibrium solutions of reactive molecules on a picosecond timescale and follow the subsequent evolution of the bi-molecular reaction with femtosecond time resolution. We study the protonation of a base (peroxynitrite) and are able to separate the diffusive encounters of the two reacting molecules from the on-contact reaction probability for protonation of the base.