Solvation beyond the linear response regime

Transient two-dimensional infrared spectroscopy (2D-IR) on a charge transfer model system is used as a nonlinear probe of solvation dynamics. Unlike what is expected in the linear response case, nonequilibrium relaxation and equilibrium spectral diffusion occur on different time scales. Transient 2D-IR spectroscopy is shown to be sensitive to higher order frequency fluctuation correlation functions, and provides evidence for a coupling between commonly observed fast and slow solvation processes.