title: Toward in Situ Measurement of the Density of Liquid Benzene Using Optical Kerr Effect Spectroscopy.
abstract: The high-frequency portion of the optical Kerr effect (OKE) spectrum of benzene shifts to higher frequency with decreasing temperature at constant pressure. This behavior has been interpreted previously in terms of an increase in librational frequencies due to the decrease in free volume with liquid densification. However, decreasing temperature also provides less access to the more repulsive portion of the intermolecular potential, which would cause the blue edge of the spectrum to red-shift. To explore the relative importance of these phenomena, molecular dynamics simulations of benzene are used to isolate the effects of temperature and density on the spectrum. The simulations show that, at constant density, the high-frequency portion of the spectrum shifts to lower frequency with decreasing temperature. In contrast, at constant temperature, the high-frequency portion of the spectrum shifts to higher frequency with increasing density. These results indicate that density plays a greater role in determining the position of the blue edge of the low-frequency Raman spectrum of benzene than does temperature. Empirical fits show that the effects of changing density or temperature are similar in experimental and simulated OKE spectra. Furthermore, line-shape analysis of simulated spectra under isochoric and isothermal conditions shows that the effects of density and temperature are separable, suggesting that OKE spectroscopy is a viable technique for in situ measurement of the density of van der Waals liquids.
authors.forename: John S
authors.initials: JS
authors.lastname: Bender
authors.forename: Samuel R
authors.initials: SR
authors.lastname: Cohen
authors.forename: Xiaoxiao
authors.initials: X
authors.lastname: He
authors.forename: John T
authors.initials: JT
authors.lastname: Fourkas
authors.affiliation: Laboratoire Interdisciplinaire de Physique (LIPhy), Université Grenoble Alpes and CNRS (UMR 5588) , F-38000 Grenoble, France.
authors.forename: Benoit
authors.initials: B
authors.lastname: Coasne