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Translational orientational correlations times

The mean diffusional structure (structure D) is that obtained with an exposure time of the order of the orientational correlation time (or of the translational counterpart) of the molecule. This structure has also been explored by computer simulation experiments,but the agreement between the results and experiment is not always satisfactory. [Pg.279]

FIGURE 2.6 (Upper panel) Plot for the reorientational correlation function against time for a representative composition (Xj = 0.1). (Lower panel) Product of the translational diffusion coefficient Dj. and the average orientational correlation time x, of the first-rank correlation function as a function of composition. Note that the solid line and dashed line indicate the hydrodynamic predictions with the stick and slip boundary conditions, respectively. [Pg.32]

Nmr methods have unrivalled potential to explore interfaces, as this account has striven to show. We have been able to determine the mobility of hydrated sodium cations at the interface of the Ecca Gum BP montmorillonite, as 8.2 ns. We have been able to measure the translational mobility of water molecules at the interface, their diffusion coefficient is 1.6 10 15 m2.s. We have been able to determine also the rotational mobility of these water adsorbate molecules, it is associated to a reorientational correlation time of 1.6 ns. Furthermore, we could show the switch in preferred reorientation with the nature of the interlayer counterions, these water molecules at the interface tumbling about either the hydrogen bond to the anionic surface or around the electrostatic bond to the metallic cation they bear on their back. And we have been able to achieve the orientation of the Ecca Gum BP tactoids in the strong magnetic field of the nmr spectometer. [Pg.404]

As we defined Tc, it represents a rotational correlation time, which is appropriate for treating intramolecular relaxation, as it is molecular orientation, not internu-clear distance, that fluctuates. Relaxation may also be mitigated by changes in internuclear distances, as molecules move relative to each other. The mathematical treatment is similar, but rc then represents a translational correlation time. [Pg.212]

ISS data have been recorded in many pure and mixed molecular liquids [34,49, 75, 83, 83-85], In most cases, the data are not described precisely by Eq. (27). Rather, an additional decay component appears at intermediate times (decay times 500 fs). This has been interpreted [49, 84] in terms of higher order polarizability contributions to C (t) which represent translational motions, an interpretation supported by observations in CCI4 (whose single-molecule polarizability anisotropy vanishes by symmetry). This interpretation is not consistent with several molecular dynamics simulations of CSj [71, 86]. An alternative analysis has been presented [82] that incorporates theoretical results showing that even the single-molecule orientational correlation function C (t) should in fact show decay on the 0.5-ps time scale of cage fluctuations [87, 88]. [Pg.28]

Incoherent neutron scattering (INS) can be used to study the translational, rotational, and vibrational motion of water protons on a time scale between 10" and 10 s. Thus INS provides data pertinent to the V structure and to the transition from the V structure to the D structure in liquid water. The principal use of INS has been to characterize the translational and rotational motion of water molecules through the interpretation of scattering data with model expressions. The three most important model parameters used are the self-diffusion coefficient, Ds, which can also be measured in an experiment involving isotope-labeled water molecules the residence time of a water molecule, tr, during which it vibrates about a fixed position before jumping to its next position and the correlation time, Ti, which is a time constant for the decay of correlation between the orientation of a water molecule at some initial time and at some later time. ... [Pg.50]

In addition, protein motion reduces the retardation of the water dynamics, because the dimension of the water translational space is increased and at the same time the decay of the orientational correlation is accelerated. In spite of this accelerated dynamics, hydration water diffusion remains anomalous for a thermalized protein. [Pg.144]

A solid matrix supplies an external field in which the potential energy U(r, 6, ) of the diatomic molecule depends on both the position r of its center of mass and its spatial orientation giwn by two angles 0 and < >. The translational and rotational degrees-of-fieedom may be coupled by means of the external field and it has to be determined to which extent tlte organic polymer matrices are capable of influencing the rotation of diatomic molecides. R ults of a Molecular Dynamics study of O2 dynamics in poly(isobutylene) (PIB) at 300 K indicate [59] that the rotation of the O2 molecules is weU separated from tlteir translational motion and the rotational correlation time x, i%0.1 ps derived from the Molecular Dynamics trajo tories [59] agrees well with the value of 0.15 ps deduced above one can conclude diat the PIB matrix d )es not affect the... [Pg.222]

Figure 15. Dynamical properties of oxygen molecules in a complete monolayer on graphite at four temperatures. Part a shows how in-plane reorientations determine the first-rank angular time-correlation-function , where a(t) is the change in in-plane orientation angle in time t, plotted on a logarithmic scale. Part b shows the average in-plane translational displacements d(t) in reduced units, obtained by dividing by o=2.46 A, plotted as a function of time in picoseconds. From Ref. [54], Langmuir 3 (1987) 581-587. Figure 15. Dynamical properties of oxygen molecules in a complete monolayer on graphite at four temperatures. Part a shows how in-plane reorientations determine the first-rank angular time-correlation-function <cos a(/)>, where a(t) is the change in in-plane orientation angle in time t, plotted on a logarithmic scale. Part b shows the average in-plane translational displacements d(t) in reduced units, obtained by dividing by o=2.46 A, plotted as a function of time in picoseconds. From Ref. [54], Langmuir 3 (1987) 581-587.
The orientational van Hove self-correlation function for the side vector of glucose (see definition in text) develops well-defined secondary peaks corresponding to rotational jumps at the same temperatures that these peaks develop in the translational VHSCF of water (see Figure 3.3 and Figure 3.4). The curves correspond to times (indicated in the figure) for which the side vector has... [Pg.51]


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See also in sourсe #XX -- [ Pg.333 , Pg.334 , Pg.335 ]




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Correlation times

Orientation correlation time

Orientation time

Orientational correlation

Time translation

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