Femtosecond time scale representative dynamics

Chapter 3 treats nuclear motions on the adiabatic potential energy surfaces (PES). One of the most powerful and simplest means to study chemical dynamics is the so-called ab initio molecular dynamics (or the first principle dynamics), in which nuclear motion is described in terms of the Newtonian d3mamics on an ab initio PES. Next, we review some of the representative time-dependent quantum theory for nuclear wavepackets such as the multiconfigurational time-dependent Hartree approach. Then, we show how such nuclear wavepacket d3mamics of femtosecond time scale can be directly observed with pump>-probe photoelectron spectroscopy. 

Femtosecond lasers represent the state-of-the-art in laser teclmology. These lasers can have pulse widths of the order of 100 fm s. This is the same time scale as many processes that occur on surfaces, such as desorption or diffusion. Thus, femtosecond lasers can be used to directly measure surface dynamics tlirough teclmiques such as two-photon photoemission [85]. Femtochemistry occurs when the laser imparts energy over an extremely short time period so as to directly induce a surface chemical reaction [86]. 

Measured RDC values are representative averages of the whole ensemble of dipolar interactions within protein molecules in solution. Such an ensemble should include all protein conformers interconverting at time scales faster than the inverse of RDC values HD). For instance, the observed dipolar coupling is affected by the intemuclei or bond vectors that stretch and vibrate on a femtosecond to nanosecond (fs-ns) time scale, the protein domain reorientation on a nanosecond to microsecond (ns-ps) time scale, and conformational change that ranges from nanoseconds, e.g., unstructured terminus, to milliseconds. It is nearly impossible to describe protein structure and dynamics using RDC values without any assumptions. Some approximations have to be made in interpreting RDC measurements. 

Abstract The time-resolved spectroscopy based on polarization effects represents one of the most sensitive techniques for studying dynamical phenomena in condensed matter. The optical Kerr effect performed with ultra-short laser pulses enables a unique investigation of dynamic processes covering a wide time range, typically from few femtoseconds up to many nanoseconds. This spectroscopic tool is particularly well suited for the measurement of relaxation patterns in complex liquids where several dynamic phenomena, taking place on different time scales, are present. In this chapter we introduce the optical Kerr effect principles, the experimental procedure, and some results from measurements in a number of different complex liquids. 

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