No abstract

The nearly degenerate asymmetric stretch vibrations near 1600 cm −1 of the guanidinium cation in D-glycerol/D 2 O mixtures having different viscosity were studied by 2D IR photon echo spectroscopy. The polarization dependent photon echo signal shows two separate frequency distributions in the 2D spectrum in D 2 O, even though only one band is evident from inspection of the linear FTIR spectrum. The split components are more clearly seen at higher viscosity. The interactions with solvent induce energy transfer between the degenerate component modes on the time scale of 0.5 ps. The energy transfer between modes is directly observed in 2D IR and distinguished by the waiting time dependence of the cross peaks from the transfers between threefold symmetric configurations of the distorted ion and solvent. The 2D IR analysis carried out for various polarization conditions required specification of frequency-frequency auto-and cross-correlation functions for the degenerate components.

Nearly degenerate asymmetric stretches with perpendicular transition dipole moments of the deuterated guanidinium cation (DGdm + ) in D 2 O and D-glycerol/D 2 O mixtures at 1600 cm −1 were investigated by linear FTIR spectroscopy and polarization dependent femtosecond pump-probe spectroscopy. The vibrational coupling of the asymmetric stretches of guanidinium occurs within 0.5 ps and leads to fast decay of the anisotropy to a level of 0.1. A systematic study of the influence of the coherence transfer on pump-probe signals is given. Following this decay the anisotropy decays with a time constant of 4.1 ps in D 2 O by rotational diffusion about an axis perpendicular to the DGdm + mean plane. The presence of aggregation was demonstrated for concentrations higher than 0.2 M.