Molecular Reorientation In Liquids Research Articles

Study of vibrational relaxation and molecular reorientation in liquids: a Raman spectroscopic study

AbstractThe vibrational relaxation and molecular reorientational processes in liquids have been studied in some carbonyl‐containing molecules using the acetonitrile (ACN) solvent. The vibrational and reorientational processes have been studied in correspondence with correlation times. The screening effect due to dielectric has been studied and the Onsager reaction field model has been tested. The study shows that repulsive types of intermolecular forces play an important role in complex systems. Copyright © 2010 John Wiley & Sons, Ltd.

The short-time dynamics of molecular reorientation in liquids. II. The microscopic mechanism of rotational friction

At short times, the dynamics of the rotational relaxation of linear molecules dissolved in liquids is governed by the instantaneous rotational friction, a quantity one can specify in complete molecular detail for each liquid configuration. Having the ability to construct such a friction is not only useful for the insight it provides into rotational dynamics, it means that it is possible to think about the superficially very different processes of rotational relaxation, vibrational population relaxation and solvation in a common language. In particular, the ability to understand the friction in molecular terms allows us to compare the actual solvent molecules participating and the actual solvent motions involved in all of these relaxation processes. In this paper we carry out a detailed study of the rotational friction felt by a homonuclear diatomic molecule dissolved in an atomic fluid, contrasting the results for a variety of solute sizes and thermodynamic states. We find remarkable levels of similarity among all three kinds of relaxation. While there are some detailed differences in the geometry of the relevant solvent motions, all three processes seem to be controlled by a small number of nearby solvents. Possibly as a result, the influence spectra (the spectral densities) of all three are virtually identical. The invariance of these findings, and indeed of the mechanistic details, to solute size and thermodynamic conditions suggests that there is a real universality to solution dynamics that comes into play when sharply varying forces are involved.

The short-time dynamics of molecular reorientation in liquids. I. The instantaneous generalized Langevin equation

Up until relatively recently, experimental measurements of the rotational dynamics of small molecules in liquids were largely confined to seeing the effects of rotational diffusion. The molecular character of the process seemed of little relevance. However, newer measurements have begun to look in some detail at the microscopics behind molecular reorientation. We show in this paper that it is possible to understand the short-time dynamics of rotation in liquids at a molecular level by looking at the instantaneous normal modes of the remaining degrees of freedom. With the aid of some other, properly short-time, approximations, the reorientational dynamics can be cast into the form of an instantaneous generalized Langevin equation—one defined for each liquid configuration. One therefore obtains fully molecular expressions for the instantaneous rotational friction and fluctuating torque felt by a solute. The average friction so obtained seems to describe the basic nondiffusional aspects of rotation reasonably accurately and lends itself—as we illustrate in the companion paper—to more detailed investigations into the actual molecular mechanisms behind rotational relaxation. In the course of this work we also show that just as the autocorrelation function for the force on a rigid bond yields an accurate portrayal of the friction needed to study vibrational relaxation, quantitatively accurate results for the rotational friction can be provided by using molecular dynamics to compute the torque autocorrelation function for an orientationally rigid solute.

Structure of MQ-NMR spin spaces under higher [formula omitted]n- and ( [formula omitted]n)↓ [formula omitted] symmetries. III. Γ/ [formula omitted] (( [formula omitted]7)↓D 5) subduced irreps for [A ] 7 clusters pertaining to the molecular cage ion, [ 11BH] 72−

Current interest in spin relaxation arising from molecular reorientation in liquids or from quantum-rotational tunnelling of molecular spin-cluster ions in solids, within the framework of Liouville, or spin-spatial product, formalisms serves to highlight the value of the symmetric group and its subduced symmetries in understanding MQ-NMR and related fields, such as single-particle inelastic neutron scattering. Combinatorial generalized wordlengths, are realizations of Rota's view of Cayley algebra of bracketed fields defining scalar invariants of spin systems, and are used in conjuctions with invariance hierarchies under the simple and direct product group algebras to generate the partitional and Γ/ Γ (( S 7)↓D 5) structures associated with the Hilbert and Liouville MQ-NMR spin bases implicit in the [A] 7/[AX] 7 cluster problems. Realization of the irreps involves consideration of the combinatorics associated with higher primes and utilising the known inner tensor products of these higher S n groups. The results derived provide insight into the higher quantum aspects of the evolution and spin dynamics of model systems, such as IF 7 and the cage molecular ion [ 11BH] 7 2−; from such properties the density operators may be expanded over the partitions or subduced irreps which leads to partitioned forms for the matrix representation of the Liouville operator. The symmetry factoring may be coupled with selective q considerations thus allowing a subset of the full spin problem to yield the significant information content of a spin problem without the necessity to consider the higher dimensioned q or [ λ ] subspaces; a conceptual parallel with the motivation underlying some of the experimental MQ-NMR work originating from the Berkeley group may be discerned.

Collision-interrupted librational model for molecular reorientation in liquids

We propose a model for molecular reorientation in liquids where the molecules have been assumed to perform libratory motion in harmonic oscillator potentials with a continuous distribution of Ubrational frequencies. The molecular rotation is interrupted by instantaneous random collision. The exact correlation functions have been calculated using a Monte Carlo technique. The calculated correlation functions exhibit the features observed in experiments. The agreement with experiment is excellent as far as the orientational correlation functions are concerned, but is not so encouraging when simultaneous agreement with angular velocity and orientational correlation functions is considered. The shortcomings of similar models proposed earlier have been discussed.

A model for strongly hindered molecular reorientation in liquids

Presentation d'un modele simple pour la reorientation fortement empechee de molecules anisotropes et utilisation dans le calcul des fonctions de correlation temps de reorientation

Tests of models of molecular reorientation in liquids

Computer simulations of tetrahedral molecules have been used to test some common models for molecular reorietation in liquids. At high density, the Fokker—Planck and J-diffusion models and a three-term Mori approximation are all unsatisfactory; the two latter provide reasonable fits at low density.

An ESR study of molecular reorientation in liquids

Electron spin resonance (ESR) has been used to study the reorientational correlation times (τ2) of a series of bis(dialkyldithiocarbamato)63 Cu(II) spin probes, in toluene, as a function of temperature. It has been found that the linear relationship τ2=C(η/T)+τ02 is obeyed over most of the temperature range studied, but at high temperatures some evidence of nonlinearity exists for the smaller spin probes. The value of C observed is intermediate between the value calculated using slip and stick boundary conditions of hydrodynamic theory. The magnitude of C is indicative of moderate non-hard-core interactions.

The Fokker–Planck–Langevin model for rotational Brownian motion. II. Comparison with the extended rotational diffusion model and with observed infrared and Raman band shapes of linear and spherical molecules in fluids

A detailed comparison of two extensions of the Debye model for molecular reorientation in liquids, Gordon’s extended J-diffusion model and the rotational Fokker–Planck–Langevin model, is presented. It is shown that the two models, although they represent very different physical pictures of rotational dynamics in fluids, lead to remarkably similar reorientational correlation functions, memory functions, correlation times and spectral densities. Only for values of the angular momentum correlation time appropriate to low density fluids do the two models give significantly different results, but the validity of the FPL model is questionable in this region. The results of an infrared study of the ν3 band of N2O in N2O/O2 along the coexistence curve from 105–153 K, and in N2O/N2 along the 80 bar isobaric line from 100–300 K are presented. The reorientational correlation functions from these measurements, and from earlier infrared studies of CO/N2 and Raman studies of CF4 and N2O liquids are compared with correlation functions computed with the EDJ and FPL models. Neither the EDJ nor the FPL model gave a substantially better description of the spectral band shape data.

A determination of the 33S quadrupole coupling constant in CS 2 from linewidth measurements

33S magnetic resonance spectra have been obtained as a function of temperature for neat liquid carbon disulfide, and the 33S quadrupole coupling constant e 2qQ h = 14.9 ± 0.3 MHz has been determined from the linewidth using previously reported reorientational correlation times. The molecular reorientation of CS 2 is discussed in terms of current hydrodynamic models for molecular reorientation in liquids.

Pac study of molecular reorientation in liquids

Pac study of molecular reorientation in liquids

Comments on high frequency molecular reorientation in liquids

The analysis of high frequency molecular reorientation in liquids is complicated by the presence of intermolecular effects. The interpretation of the data in terms of angular velocity correlation functions and dynamic molecular models is often subject to uncertainties due to slight differences in the definitions of relevant correlation functions and times. A brief discussion of some of these problems is presented.

Molecular reorientation in liquids by Rayleigh scattering: Pressure dependence of rotational correlation functions

Results of high pressure study of the depolarized Rayleigh scattering in acetone, benzene, and methyl iodide are presented. The density dependences of the angular velocity and angular position correlation functions are determined. The angular velocity correlation function of each liquid shows a negative overshoot. In addition, benzene at all pressures and methyl iodide at high pressures exhibit additional oscillations in the angular velocity correlation function. The details of the correlation functions are discussed in terms of ''collision interrupted'' models such as the well known J-diffusion model. It is concluded that a more general description than J diffusion capable of allowing incomplete loss of momentum upon collision is needed. The results are compared to studies of reorientation by means of NMR. Finally, the relation between shear viscosity and reorientation in these liquids is discussed.

ChemInform Abstract: MOLECULAR REORIENTATION IN LIQUIDS, EXPERIMENTAL TEST OF HYDRODYNAMIC MODELS

Chemischer InformationsdienstVolume 6, Issue 2 Physical Organic Chemistry ChemInform Abstract: MOLECULAR REORIENTATION IN LIQUIDS, EXPERIMENTAL TEST OF HYDRODYNAMIC MODELS D. R. BAUER, D. R. BAUERSearch for more papers by this authorJ. I. BRAUMAN, J. I. BRAUMANSearch for more papers by this authorR. PECORA, R. PECORASearch for more papers by this author D. R. BAUER, D. R. BAUERSearch for more papers by this authorJ. I. BRAUMAN, J. I. BRAUMANSearch for more papers by this authorR. PECORA, R. PECORASearch for more papers by this author First published: January 14, 1975 https://doi.org/10.1002/chin.197502102Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume6, Issue2January 14, 1975 RelatedInformation

Comparison of diffusion and strong collision models for molecular reorientation in liquids: simulated electron spin resonance spectra for spin systems of varying multiplicity

E.s.r. spectra for spin systems of different multiplicity have been simulated using diffusion and strong collision models for molecular reorientation. The strong collision parameter k has been varied in an attempt to find the best agreement between spectra simulated using the different models. In adopting complex values of k which give simulated spectra most similar to diffusion calculations, it is found that the variation in k is a function not only of correlation time but also of the multiplicity of the spin system and the magnitude of the spin interaction parameters.

Molecular reorientation in liquids. Experimental test of hydrodynamic models

Molecular reorientation in liquids. Experimental test of hydrodynamic models

Raman spectroscopy and molecular reorientation in liquids: CDCl3 and CH3Br

Raman scattering experiments on symmetrical stretching lines of liquid CDCl3 and CH3Br have been carried out at room temperature. Angular autocorrelation functions were calculated by Fourier transforming the spectra, and by eliminating the vibrational correlation function. It is found that vibrational relaxation contribution to band shapes is important for these molecules. Correlation times were found to be τ2 = 1.59 ± 0.03 psec for CDCl3 and 1.33 ± 0.07 psec for CH3Br, in agreement with previous results obtained in different ways. The times between collisions were found to be much shorter (∼ 0.01–0.03 psec) than those obtained by infrared absorption experiments but in fair agreement with recent results obtained by Bartoli and Litovitz. Second moments were found to be smaller than those predicted for pure rotational Raman bands in the classical limit. The last result may partly be explained by the important contribution of the vibrational relaxation to the band shape.

Angular Time-Correlation Functions from Spectra for Some Molecular Liquids

Depolarized Rayleigh wing scattering data are reported for liquid chloroform, methyl iodide and methylene chloride. The calculation of orientation correlation functions from these results and from infrared vibration-rotation bands is discussed. Fourier transforms of the infrared bands are corrected for shape changes due to variable refractive index, isotope splitting and hot bands. The resulting correlation functions are primarily a measure of orientational and collision-induced changes in polarizability or dipole moment. It is argued that the collision-induced contributions are important only at short times. The long-time behavior of the correlation functions is then compared with several models for molecular reorientation in liquids, and it is concluded that the motion of these molecules is probably best characterized by models involving random walks in angular momentum space.

Theory of Molecular Reorientation in Liquids II: ESR Line Shapes for Slow Anisotropic Rotation

AbstractThe master equation approach to molecular reorientation in liquids is discussed with respect to ESR line shapes. The example of a non axially symmetric g‐tensor is considered for slow molecular reorientation by anisotropic rotational diffusion, and rotational jumps. The rotational jump model with arbitrary step length is augmented by an additional term which allows for anisotropic motions.

Molecular Reorientation in Liquids and Gases

In this paper two simple criteria for guessing the time-dependent orientational distribution function from the experimentally measured dipolar autocorrelation function 〈u(0)·u(t) 〉 are examined. The first maximizes the information entropy of the distribution under the constraint imposed by the known 〈u(0)·u(t) 〉, and the second minimizes the mean-square difference between the distribution function and the equilibrium (t → ∞) distribution under the same constraint. The accuracy of these criteria is tested on the results of computer studies of the rotational relaxation of diatomic liquids. The same general method is applied to the Van Hove self-correlation function, and to the center-of-mass velocity transition probability.