Vibrational dynamics of the CN stretching mode of [Ru(CN)6]4- in D2O studied by nonlinear infrared spectroscopy

We have studied vibrational dynamics of the T (1u) mode of the CN stretching mode of [Ru(CN)(6)](4-) in D2O by infrared (IR) nonlinear spectroscopy such as an IR three-pulse photon echo experiment and polarization-sensitive IR pump-probe spectroscopy. The isotropic component of the pump-probe signal shows a bi-exponential decay with time constants of 0.8 ps and 20.8 ps. The fast and slow components correspond to the rapid equilibration between the T (1u) mode and the Raman active modes of the CN stretching mode and the vibrational population relaxation from the nu = 1 state of the T (1u) mode, respectively. Anisotropy of the pump-probe signal decays with a time constant of 3.1 ps, which is due to the time evolution of the superposition states of the triply degenerate T (1u) modes. Three pulse photon echo measurements showed that the time correlation function of the frequency fluctuation decays bi-exponentially with time constants of 80 fs and 1.4 ps. These time constants depend only on the solute and are independent of the solvent, whereas the amplitudes depend on both the solute and solvent.