Relaxation effects, intermolecular

Intermolecular Relaxation Effects in the Ultraviolet Photoelectron Spectroscopy of Molecular Solids... 

Intermolecular relaxation effects are a central issue in the interpretation of the ultraviolet photoelectron spectroscopy (UPS) of molecular solids. These relaxation effects result in several significant characteristics of UPS valence spectra, intermolecular relaxation phenomena lead to localized electron molecular-ion states, which are responsible for rigid gas-to-solid molecular spectral energy shifts, spectral line broadening, and dynamic electronic localization effects in aromatic pendant group polymers. 

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

The surface effect discussed above is an aspect of inter-molecular relaxation in molecular solids is that associated with the depth of the molecule from the sample surface. This effect manifests itself as an apparent line-broadening in UPS spectra, other contributions to line-broadening also exist. These, as well as some specific mechanisms that lead to the observed intermolecular polarization effect will be discussed below. 

In a condensed molecular solid, however, there are also intermolecular relaxation (polarization) effects that occur in addition to the intramolecular effects (1, 11), as discussed above. In fact, in any dielectric medium, the total net positive charge density on the molecular cation induces corresponding electronic, and ultimately atomic, distortions in the surrounding medium. 

Abstract For three liquids, salol, propylene carbonate, and o-terphenyl, we show that the relaxation time or the viscosity at the onset of Arrhenius behavior is a material constant. Thus, while the temperature of this transition can be altered by the application of pressure, the time scale of the dynamics retains a characteristic, pressure-independent value. Since the onset of an Arrhenius temperature-dependence and the related Debye relaxation behavior signify the loss of intermolecular constraints on the dynamics, our result indicates that intermolecular cooperativity effects are governed by the time scale for structural relaxation. 

On the basis of the results of the dynamics simulation of liquid water it turns out that the VB like wavefunction based on the SCF-MI non-orthogoml occupied and virtual orbitals, describes accurately the intermolecular potential of water. Exclusion of BSSE in an <7priori fashion is ensured and geometry relaxation effects are naturally taken into account. 

In terms of intramolecular flexibility, the poly(2,6-disub-stituted-1,4-phenylene oxides) are freely rotating chains [71] however, intermolecular steric effects may limit phe-nylene rotation in the solid state and periiaps account for the absence of detectable sub-Tg relaxational processes. For example, results of NMR measurements indicate that the phenylene rings of PPO can execute only small amplitude motions due to the relative stiffness and dense packing of the PPO chain and blockage from rings on adjacent chains. 

According to the coupling model, for neat polymers at the times appropriate for most experimental measurements, the slowing down of segmental relaxation gives rise to a correlation function having the form of equation (1). The stretch exponent is a measure of the strength of the intermolecular constraints on the relaxation. These constraints depend on molecular structure because the chemical structure determines the intermolecular interactions. However, the complexity of cooperative dynamics in dense liquids and polymers precludes direct calculation of P it is invariably deduced from experiment. An assumption fundamental to the model is that the time at which intermolecular cooperativity effects become manifest is independent of temperature. 

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. 

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