Translational-rotational coupling

The issue of the relationship between rotational dynamics and the distribution of charge and mass in a molecular ion has seen some attention in studies of high temperature fused salts, most notably cyanide-containing species. Experimental [184] and theoretical [185] studies note complex rotational relaxation dynamics for these systems. These phenomena have been interpreted with the framework of rotational-translational coupling [186], a more detailed but less transparent description than the charge arm framework described above. This may be a useful approach to understanding IL dynamics, but has not to our knowledge been applied to these systems. 

In view of these results for binary glasses composed of molecules with different masses respectively different Tg, one may speculate that the isotropic reorientation of the small molecules results from translational diffusion in an essentially rigid glassy matrix formed by the large molecules, i.e., the diffusional process may be probed by 2H NMR via rotational-translational coupling.183 Finally, we note that the stimulated-echo technique was also applied to study the main relaxation in... 

In Section IV the computer simulation is extended to describe the effects of excitation in chiral molecules and racemic mixtures of enantiomers. The modification of the dynamical properties brought about by mixing two enantiomers in equimolar proportion may be explained in terms of rotation-translation coupling. The application of an external field in this context ai iplifies the difference between the field-on acf s and cross-correlation of enantiomer and racemic mixture and provides a method of studying experimentally the fundamental phenomenon of rotation-translation coupling in the molecular liquid state of matter. 

Rotation-translation coupling was neglected when the molecules were moving, that is, translation did not imply rotation and vice-versa. 

It has recently become more widely appreciated that the presence of rotational diffusional anisotropy in proteins and other macromolecules can have a significant affect on the interpretation of NMR relaxation data in terms of molecular motion. Andrec et al. used a Bayesian statistical method for the detection and quantification of rotational diffusion anisotropy from NMR relaxation data. Sturz and Dolle examined the reorientational motion of toluene in neat liquid by using relaxation measurements. The relaxation rates were analyzed by rotational diffusion models. Chen et al measured self-diffusion coefficients for fluid hydrogen and fluid deuterium at pressures up to 200 MPa and in the temperature range 171-372 K by the spin echo method. The diffusion coefficients D were described by the rough sphere (RHS) model invoking the rotation translational coupling parameter A = 1. 

There are three translational dispersion curves and three rotational dispersion curves. In the absence of rotation-translation coupling these vibrations are also distinctly separate. However, external modes and internal modes of the same character will become mixed, the closer they are in frequency the greater will be the mixing. Atomic displacements are no longer controlled by exclusively internal or external forces but by both. Modes of a mostly internal (or mostly external) character now involve displacements of the centre of mass (or deformations of the molecular frame). This is a general feature of all molecular crystals but it is usual to ignore such complications when the frequency of the lowest... 

Phonons and librons in herringbone and pinwheel commensurate and incommensurate N2 monolayers on graphite were investigated based on quantum-mechanical mean-field and time-dependent Hartree methods for the ground state [19]. The latter method includes on a systematic basis rotation-translation coupling which is neglected within the mean-field approximation, and it is able to treat motions with larger (but still finite) amplitudes around... 

Equations (3.12)-(3.15) do formally apply for rigid rods too, when the hydrodynamic interaction term H(q) is replaced by a term Cg(q) originating from the rotational relaxation of rigid rods which differs numerically only from the function H(q) given above. Eventually the numerical coefficient C in Eq. (3.15) becomes C = 1/30 and C = 0.1 with and without consideration of rotation-translation coupling, respectively [183]... 

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