Vibrational spectral diffusion of CN− in water

We present 2D-IR spectra of a weak IR absorber, 13 C 15 N − dissolved in D 2 O, by means of heterodyne detected three-pulse photon echo experiments. Spectral dephasing of the stretch vibration of the cyanide ion is governed by two processes: A fast, inertial process which is essentially in the homogeneous limit, and which gives rise to the larger fraction of the total line-width of the transition (≈10 cm −1 ), and an additional slower spectral diffusion process with 5.3 cm −1 line-width and 2.9 ps time constant. We consider this molecule a benchmark system to optimize theoretical approaches to describe vibrational dephasing of strongly interacting solute–solvent systems.