High pressure cell to measure the depolarization ratio of the light scattered by gases

Abstract

2014 On présente un appareillage facile à réaliser permettant de mesurer des taux de dépolarisation supérieurs à 10-4. La principale difficulté rencontrée vient de la biréfringence accidentelle. Nous indiquons comment la minimiser par construction mécanique et comment tenir compte de la biréfringence résiduelle par un calcul et des contrôles appropriés.Abstract. 2014 An easily assembled apparatus permitting the measurement of depolarization ratio higher than 10-4 is presented. The major difficulty arises from the depolarization, due to the birefringence of the windows under stress. We explain how to minimize it by mechanical means, and how to deal with the problem of residual birefringence by appropriate calculation and tests.

Calculations of second light-scattering virial coefficients of linear and quasi-linear molecules

“…Much more favourable are gases like CO, CH3F and CHF3, which not only have tao 4~ Light-scattering virial coefficients 307 sity effects have been made is ethylene, where the data are presented by Berrue et al [9] in the form of a small graph of depolarization ratio versus pressure, observed at 328 K. The wavelength is not stated, but was probably 514-5 nm as used in subsequent work [11]. From the graph we deduce that Bp =-2.2x 10-6m3mo1-1.…”

“…The presence of B in equation (2) [8], and may be the reason that very few measurements of Bp for anisotropic molecules have been undertaken. Nitrogen, which has a small B value of only -4-2 x 10 .6 m 3 tool -1 at 300 K, and which exhibits a Gp nearly five times this value, has been recognized as a favourable molecule to investigate experimentally [8,9] and theoretically [10,11]. Berrue, Chave, Dumon, and Thibeau [10,11] present expressions for the Gp contribution to Bp which include angular correlation and collision-induced anisotropy, but in their evaluation of the latter they neglect the polarizability anisotropy in successive dipole-induced-dipole interactions.…”

Calculation and measurement of the second light-scattering virial coefficients of nonlinear molecules: a study of ethene

“…In 1977, Berrue et al [10] made measurements of light-scattering density effects of ethene at 328 K, presenting their data in the form of a small graph of depolarization ratio versus pressure. The wavelength of the incident light was not stated, but was Experimental depolarization ratio as a function of gas density for ethene using the data of Berrue et al [10].…”

“…The wavelength of the incident light was not stated, but was Experimental depolarization ratio as a function of gas density for ethene using the data of Berrue et al [10].…”

“…Consequently, Bp appears to suffer an inherent disadvantage that when the 2B component predominates, it becomes difficult to extract precise values of ~ from experimental values of Bp. Before 1993, experimental measurements of Bp for only four non-spherical gas molecules had been reported, namely: nitrogen [7,8], carbon dioxide [8], carbonyl sulphide [8] and ethene [10]. A complete theory permits the choice of molecules which have a favourable ratio (~/2B).…”