Vibrational and structural dynamics of two transition metal carbonyl complexes, Mn（CO）5Br and Re（CO）5Br were examined in DMSO, using ultrafast infrared pump-probe spectroscopy, steady-state linear infrared spectroscopy and quantum chemistry computations. Two car- bonyl stretching vibrational modes （a low-frequency A1 mode and two high-frequency degenerate E modes） were used as vibrational probes. Central metal effect on the CO bond order and force constant was responsible for a larger E-A1 frequency separation and a generally more red-shifted E and A1 peaks in the Re complex than in the Mn complex. A generally broader spectral width for the A1 mode than the E mode is believed to be partially due to vibrational lifetime effect. Vibrational mode-dependent diagonal anharmonicity was observed in transient infrared spectra, with a generally smaller anharmonicity found for the E mode in both the Mn and Re complexes.
Canonical Watson-Crick base pairs and four representative mismatched base pairs have been studied by quantum chemical computations. Detailed anharmonic vibrational analysis was carried out to reveal some vibrational signatures characteristic of structural aspects of the base monomers and dimers, which were well manifested in simulated 1D IR and 2D IR spectra. The degree of delocalization of the selected normal modes, represented by the potential energy distribution, was found to vary sig-nificantly from isolated bases to H-bonded dimers, and was accompanied by changes in anharmonicities of these modes. Examples are given for the generally accepted carbonyl stretching mode of base pairs appearing in the 6-m wavelength region of IR spectra.
