Collision-Induced Effects on the Dielectric Properties of Liquid Dimethylsulfoxide

Abstract

É apresentado um estudo por simulação de dinâmica molecular das propriedades dielétricas do dimetil sulfóxido líquido, onde são incluídos efeitos de indução devido à polarizabilidade molecular através de perturbação em primeira ordem. Neste formalismo, os dipolos induzidos são computados a partir de trajetórias geradas pelos potenciais intermoleculares isentos de forças indutivas. Propriedades dielétricas estáticas e dinâmicas são computadas para as versões polarizável e nãopolarizável da densidade dipolar. As análises indicam que o principal papel das componentes de indução nesta abordagem é o de renormalizar o valor das flutuações estáticas dos dipolos permanentes, sendo apenas marginal a influência sobre as propriedades de relaxação no regime de difusão rotacional que caracteriza o espectro na região de micro-ondas. Entretanto, para maiores frequências, onde a absorção dielétrica é predominantemente determinada por movimentos intermoleculares libracionais, os efeitos dinâmicos da polarizabilidade molecular são mais aparentes. Na presença de contribuições indutivas, o máximo do espectro infravermelho obtido das simulações está em melhor concordância com recentes medidas espectroscópicas da dinâmica intermolecular deste líquido. We present a molecular dynamics (MD) simulation study of the dielectric properties of liquid dimethyl sulfoxide that includes interaction-induced effects due to molecular polarizability using a perturbative scheme in which the induced dipoles are computed a posteriori from the MD trajectories generated without explicit inductive forces. Static and dynamical quantities of relevance to the dielectric characterization of the liquid are reported for both polarizable and nonpolarizable versions of the system's collective dipolar densities. Our analysis within this scheme indicates that the role of the interaction induced contributions is predominantly to renormalize the magnitude of the permanent dipole fluctuations, with marginal effects upon the system's dielectric relaxation in the rotationaldiffusion, microwave region of the spectrum. At higher frequencies, however, where the dielectric absorption is dominated by fast intermolecular librational motions, the dynamical effects of the molecular polarizability are more pronounced. In the presence of interaction induced contributions, the location of the peak in the MD far infrared absorption coefficient is in much better agreement with recent spectroscopic measurements of the intermolecular dynamics of this liquid.

On Intermolecular Dipolar Coupling in Two Strongly Polar Liquids: Dimethyl Sulfoxide and Acetonitrile

“…The reason for that unexpected difference in the static permittivity (ε s DMSO ≈ 1.3ε s ACN ) must results from an essential difference in the molecular dipoleÀdipole coupling abilities occurring in liquid DMSO and ACN. The conclusion is strongly supported by the Kirkwood correlation factor (g K ) measurements which gave for DMSO the following results: g K DMSO = 1.01, 13,18 0.99, 40 1.13, 41 1.00, 42,43 0.95, 44 and 1.04 45 what quite clearly points out for the lack of the dipolar coupling in that liquid, whereas for ACN, the values are g K ACN = 0.74, 41 0.75, 46 and 0.82, 47 as expected for the liquid with molecular antiparallel dipoleÀdipole coupling.…”

“…Industrially, ACN is used, among others, as a solvent for the manufacture of pharmaceuticals and photographic films. No wonder that both compounds are the subject of numerous studies both experimentally − and theoretically. − …”

Dipolar Self-Assembling in Mixtures of Propylene Carbonate and Dimethyl Sulfoxide as Revealed by the Orientational Entropy

“…Immediately striking is the significantly different behavior of the increment in neat liquids. In the case of PC, we are undoubtedly faced with a phenomenon of head-to-tail association of dipoles, whereas DMSO demonstrates, as expected, the virtual absence of aggregation of molecular dipoles. − …”

“…On the basis of the above values of ε ∞ , the calculated Kirkwood correlation factor g K equals either 1.23 (which points to the not too high but clear linear association of the head-to-tail type) or 0.57 (strongly antiparallel association). A slightly smaller, but also confusing, discrepancy concerns the dipolar association in DMSO, for which extreme values of g K of 0.52 or 1.04 can be found; however, most published data are not far from g K = 1. − …”

Intermolecular Structure and Collective Dynamics of Supercritical Fluoroform Studied by Molecular Dynamics Simulations

“…Dielectric relaxation in fluids of highly polar molecules is often dominated by the collective reorientation mechanism. ,− In addition to M 0 , a portion of M I relaxes via this mechanism. This portion can be identified by projecting M I along M 0 , using a scheme adopted from DLS. , The part of Φ( t ) that relaxes via collective reorientation is normalΦ RR ( t ) = false( 1 + G false) 2 normalΦ 00 ( t ) where G = false⟨ boldM normalI ( 0 ) · boldM 0 ( 0 ) false⟩ ⟨ | M 0 | 2 ⟩ = normalΦ 0 normalI ( 0 ) 2 normalΦ 00 ( 0 ) is the projection and (1 + G ) 2 acts as a local field factor, as a rescaling of M 0 by (1 + G ).…”