Relaxation intermolecular

Smith, G.D. and Boyd, R.H. (1992) Subglass relaxations - Intermolecular packing and the relaxation-times for ester side group reorientation - a Molecular-dynamics simulation. Macromolecules 25,1326-1332. Mani, R. and Burns, C.M. (1991) Homo- and copolymerization of ethylene and styrene using TiCl ... 

McMorrow D and Lotshaw WT 1991 Dephasing and relaxation in coherently excited ensembles of intermolecular oscillators Cham. Phys. Lett. 178 69-74... 

The high degree of resolution in the CP/MAS NMR spectra also permits the analysis of the relaxation behaviour of individual carbon atoms. The T1 relaxation is seldom solely determined by a single motion of a single intermolecular interaction. Nevertheless, if the dominant source is known, T1 can provide useful information. As an example the relaxation behaviour of celluloseacetate in both acetone solution and in the solid state will be discussed. The experimental data in Table 2 give chemical shifts and relaxation T1 information for the above system 21 . 

Recent reports 54 seem to indicate that the resolution of the notoriously difficult solid-state spectra of coals may be enhanced by such techniques as double exponential multiplication and convolution difference. Differential relaxation behaviour as discussed in connection with intermolecular effects in carbohydrates and low temperature methods may further improve identification. 

Since we are interested in this chapter in analyzing the T- and P-dependences of polymer viscoelasticity, our emphasis is on dielectric relaxation results. We focus on the means to extrapolate data measured at low strain rates and ambient pressures to higher rates and pressures. The usual practice is to invoke the time-temperature superposition principle with a similar approach for extrapolation to elevated pressures [22]. The limitations of conventional t-T superpositioning will be discussed. A newly developed thermodynamic scaling procedure, based on consideration of the intermolecular repulsive potential, is presented. Applications and limitations of this scaling procedure are described. 

Here, is the magnetization of spin i at thermal equilibrium, p,j is the direct, dipole-dipole relaxation between spins i and j, a-y is the crossrelaxation between spins i and j, and pf is the direct relaxation of spin i due to other relaxation mechanisms, including intermolecular dipolar interactions and paramagnetic relaxation by dissolved oxygen. Under experimental conditions so chosen that dipolar interactions constitute the dominant relaxation-mechanism, and intermolecular interactions have been minimized by sufficient dilution and degassing of the sample, the quantity pf in Eq. 3b becomes much smaller than the direct, intramolecular, dipolar interactions, that is. 

Cross-relaxation The mutual intermolecular or intramolecular relaxation of magnetically equivalent nuclei, e.g., through dipolar relaxation. This forms the basis of nOe experiments. 

Intermolecular relaxation has little effect on intra-peptide exchange-transferred NOE intensities. J. Biomol. NMR 2002,... 

First approaches to approximating the relaxation time on the basis of molecular parameters can be traced back to Rouse [33]. The model is based on a number of boundary assumptions (1) the solution is ideally dilute, i.e. intermolecular interactions are negligible (2) hydrodynamic interactions due to disturbance of the medium velocity by segments of the same chain are negligible and (3) the connector tension F(r) obeys an ideal Hookean force law. 

Xantheas, S.S. (1996) On the importance ofthe fragment relaxation energy terms in the estimation of the basis set superposition error correction to the intermolecular interaction energy, J. Chem. Phys., 104, 8821-8824. 

Electronic transitions in a solute take place very fast, i.e., almost immediately in comparison with the movement of the molecules as a whole and vibrations of atoms in organic molecules. Hence, absorption and fluorescence can be denoted in Fig. 5 by vertical arrows, in accordance with Franck-Condon principle. Both these processes are separated by relaxations, which are intermolecular rearrangements of the solute-solvent system after the excitation. 

For excitation of solutes with 0-0 transitions v0o>v (antiStokes spectral region of absorption), the situation is the opposite at the initial instant of time, the spectra are red-shifted as compared to the steady state spectra, Av1 (l)<0. In this case, the return of the spectrum to its normal position during configurational relaxation will lead to a blue shift with time. From the physical point of view, this means that the intermolecular energy excess, which the solvates possess before excitation, is partially converted into emitted energy leading to an increase in the radiation frequency with time. That is why the process may be called the up-relaxation of the fluorescence spectra. 

Minima in Ti are usually above the So hypersurface, but in some cases, below it (ground state triplet species). In the latter case, the photochemical process proper is over once relaxation into the minimum occurs, although under most conditions further ground-state chemistry is bound to follow, e.g., intermolecular reactions of triplet carbene. On the other hand, if the molecule ends up in a minimum in Ti which lies above So, radiative or non-radiative return to So occurs similarly as from a minimum in Si. However, both of these modes of return are slowed down considerably in the Ti ->-So process, because of its spin-forbidden nature, at least in molecules containing light atoms, and there will usually be time for vibrational motions to reach thermal equilibrium. One can therefore not expect funnels in the Ti surface, at least not in light-atom molecules. 

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