A comparison of ultrafast vibrational dynamics in liquids, glasses, and proteins.

摘要

Some good demonstrations of the powerful scientific uses of the vibrational echo technique are demonstrated in this thesis. The vibrational echo pulse technique, combined with pump probe or transient absorption experiments, probe molecular motions on their time scale allowing scientists to gain insights into the important inter- and intramolecular interactions. The interactions on this time scale ultimately control many classes of chemical reactions and processes.;Vibrational echo and pump-probe experiments require ultrafast, tunable infrared laser pulses. Data is presented performed using the Stanford Medical Free Electron Laser and using a Ti:Sapphire based optical parametric amplifier system. Similarities and differences between these two very different experimental systems are discussed.;Complete temperature dependent vibrational echo studies are presented on Rh(CO)2acac and W(CO)6 in dibutyl plithalate. The mechanism attributing to the low temperature dephasing of both chromophores is phonon assisted tunneling between two level systems. At high temperatures, thermal activation of the M-C (M=Rh,W) mode, and the resulting change in backbonding, is the dominant source of dephasing.;A series of vibrational echo studies of CO at the active site of the proteins myoglobin and hemoglobin are presented. In the protein studies, the dephasing mechanism at low temperature is essentially the same as for the Rh(CO)2acac and W(CO)6. However, myoglobin studies in a variety of solvents indicated that at high temperature, the protein undergoes a transition that enables motions which cause a temperature dependent dephasing different from the power laws or Arrhenius behavior seen in the inorganic systems. Studies of two myoglobin mutants suggests that it is the fluctuating electric fields felt at the heme that cause the dephasing.;The use of the vibrational echo technique to measure spectra, rather than dynamics is illustrated theoretically and experimentally. The time evolution of the system allows spectral contrast between various vibrational modes. Some theoretical examples are presented and two experimental results are presented.;Slight changes in experimental conditions allow the vibrational echo technique to probe the pure dephasing width and lifetime of higher order modes of a system. This technique also allows for a direct measurement of the anharmonicity of a vibration.