Femtosecond spectroscopy, ultrafast dynamics

Femtosecond spectroscopy has an ideal temporal resolution for the study of ultrafast water motions from femtosecond to picosecond time scales [33-36]. Femtosecond solvation dynamics is sensitive to both time and length scales and can be a good probe for protein hydration dynamics [16, 37-50]. Recent femtosecond studies by an extrinsic labeling of a protein with a dye molecule showed certain ultrafast water motions [37-42]. This kind of labeling usually relies on hydrophobic interactions, and the probe is typically located in the hydrophobic crevice. The resulting dynamics mostly reflects bound water behavior. The recent success of incorporating a synthetic fluorescent amino acid into the protein showed another way to probe protein electrostatic interactions [43, 48]. 

With the intensive development of ultrafast spectroscopic methods, reaction dynamics can be investigated at the subpicosecond time scale. Femtosecond spectroscopy of liquids and solutions allows the study of sol-vent-cage effects on elementary charge-transfer processes. Recent work on ultrafast electron-transfer channels in aqueous ionic solutions is presented (electron-atom or electron-ion radical pairs, early geminate recombination, and concerted electron-proton transfer) and discussed in the framework of quantum theories on nonequilibrium electronic states. These advances permit us to understand how the statistical density fluctuations of a molecular solvent can assist or impede elementary electron-transfer processes in liquids and solutions. 

C. Woywod, W. Domcke, A. L. Sobolewski, and H-J Werner, Characterization of the 5,-5 conical intersection in pyrazine using ab initio multiconfiguration self-consistent-field and multireference configuration-interaction methods, J. Chem. Phys. 100 1400 (1994) G Stock and W. Domcke, Femtosecond spectroscopy of ultrafast nonadiabatic excited-state dynamics on the basis of ab initio potential-energy surfaces the S2 state of pyrazine, J. Phys. Chem. 97 12466 (1993). 

Investigation of ultrafast dynamics and spectroscopy of anionic systems and biologically relevant species using femtosecond laser sources. 

Since then the ultrafast dynamics of a few molecular, especially dimer, systems have been studied. Zewail observed the vibrational and rotational revival of excited I2 [21-23]. Stolow studied the same system, applying femtosecond pump probe zero-kinetic-energy (ZEKE) photoelectron spectroscopy [24, 25]. Gerber observed fascinating features in the ultrafast dynamics of the sodium dimer s multiphoton ionization (MPI) (see Fig. 1.1a), induced... 

For the bound Naa B system, 1.25 ps and 120 fs one-color real-time TPI spectroscopy, at moderate intensities, yielded preferential excitations of the relatively slow pseudorotation (3 ps) and the fast symmetric stretch mode (310 fs) respectively. Three-dimensional quantum chemical and quantum dynamical ab initio investigations fully corresponded to these experimental results. The time-dependent wave packet dynamics elucidate the effect of ultrafast state preparation on the molecular dynamics. Hence, these experiments manifest efficient control of molecular dynamics using the pulse duration as a control parameter. Since known cw spectra show the pseudorotation features only, this result demonstrates also that cw and femtosecond spectroscopy have complementary sensitivities for the excitation of different vibrational modes, thus neatly confirming the original conjecture of Zewail (see e.g. [425]). 

G. Stock and W. Domcke, Femtosecond Spectroscopy of Ultrafast Nonadia-batic Excited-State Dynamics on the Basis of APotential-Energy Surfaces The S2 State of Pyrazine , J. Phys. Chem. 97, 12 466 (1993). 

E. Schreiber, R.S. Berry, T. Leisner, S. Rutz, S. Wolf, and L. Woste, Femtosecond Dynamics of the Ground State of Aga A New Approach to Study the Ultrafast Dynamics of Mass-Selected Neutral Clusters in Ultrafast Processes in Spectroscopy, O. Svelto, D. De Silvestri, and G. Denardo (eds.) (Plenum, New York, 1996), pp. 133-137. 

Femtosecond Real-Time Spectroscopy of Small Molecules and Clusters attempts to give a detailed overview of a small part of this new and exciting field situated at the boundary between physics and chemistry. The main subject of this book is research into the ultrafast dynamics of gas-phase molecules and clusters after excitation with intense femtosecond or picosecond laser pulses. Many textbook-like examples are presented. 

Underwood, D. E., Kippeny, T. and Rosenthal, S. J. (2001) Ultrafast carrier dynamics in CdSe nanocrystals determined by femtosecond fluorescence upconversion spectroscopy. /. Phys. Chem. B, 105,436-443. 

Recently, Zewail and co-workers have combined the approaches of photodetachment and ultrafast spectroscopy to investigate the reaction dynamics of planar COT.iii They used a femtosecond photon pulse to carry out ionization of the COT ring-inversion transition state, generated by photodetachment as shown in Figure 5.4. From the photoionization efficiency, they were able to investigate the time-resolved dynamics of the transition state reaction, and observe the ring-inversion reaction of the planar COT to the tub-like D2d geometry on the femtosecond time scale. Thus, with the advent of new mass spectrometric techniques, it is now possible to examine detailed reaction dynamics in addition to traditional state properties." ... 

Seel, M., and Domcke, W. (1991), Femtosecond Time-resolved Ionization Spectroscopy of Ultrafast Internal-Conversion Dynamics in Polyatomic Molecules Theory and Computational Studies, J. Chem. Phys. 95,7806. 

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