Field-cycling molecular motion

Field-cycling NMR relaxometry is a versatile and powerful method for investigating molecular dynamics over a large range of timescales. It has been applied to manifold materials which show broad distributions of molecular motions, for example proteins, liquid crystals, synthetic polymers, and liquids confined in porous materials. Figure 7A represents an example for the investigation of polymer dynamics. The T -dispersion curve in the double-logarithmic scale shows the typical slopes observed in polyethylene oxide melts above the critical molecular... 

Fig. 5. Schematic representation of the experimental temperature/frequency window conveniently accessible by field-cycling NMR relaxometry in combination with conventional high-field techniques. It specifically addresses the chain-mode regime of typical polymers, whereas local segment fluctuations and center-of-mass motions can only be probed at low temperatures/high frequencies and high temperatures/low fi-equencies/low molecular weights combinations, respectively...

If this expected photoemission really takes place, the resultant spectra should reflect the nonhnear dynamics of nonadiabatic vibrational motion under an external field, which is similar to classical driven oscillators such as a forced Duffing oscillator [156, 239]. Therefore various nonlinear phenomena such as limit cycle, frequency locking, and chaos (1.5-dimensional chaos) [156, 239] can be expected, which would be intrinsically originated from the quantmn dynamics. Furthermore, one may be able to control the frequency and amplitude of the photoemission by varying the laser parameters applied. It may be possible to utilize the photoemission as a new optical somce and also as finger-print signals to identify molecular species and/or molecular states. In this section we illustrate the appearance of such... 

Direct control on the electron dynamics has become a hot topic. It requires changes in the electric field on a further shorter time. Two different strategies relying either on the CEP or on the temporal phase in a modulated light field are shortly presented. In the first strategy the CEP of a few-cycle pulse is varied to control the electron dynamics. The second strategy relies on the highly precise temporal phase control in a multi-pulse sequence [79]. The theoretical treatment requires the simultaneous description of electronic and vibrational wavepacket motion. The fundamental steps of our approach [80] for molecular systems are shortly reviewed. 

Intense THz magnetic field pulses allowed not only the induction of spin precession but also its extinction on demand. This was achieved by exciting the sample by a pair of THz pump pulses which were delayed with respect to one another the second, delayed pulse induced a precessional motion that was out of phase with the precession due to the first pulse, and thereby stopped the spin precession. This is shown in Figure 6.15(e) for a pump pulse pair delayed by 6.5 precession cycles. Similar sequences of pulses (of much lower frequencies) have been used in nuclear spin resonance to investigate molecular structure. The extension to the THz domain (THz-ESR) would require, however, magnetic field strengths about 100 times stronger than currently available in the Department. 

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