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.

Low-Frequency (Gigahertz to Terahertz) Depolarized Raman Scattering Offn-Alkanes, Cycloalkanes, and Six-Membered Rings: A Physical Interpretation

“…The librational amplitudes decrease slightly with decreasing temperature, which could be explained by liquid densification producing a reduction in the average angle of libration. Librational frequencies increase on cooling, an effect observed previously in experimental and simulated OKE studies on benzene . This is again attributed to the increasing liquid density, where less free space means less free motion of a molecule in a cage, and intermolecular potential landscapes become more quadratic in nature.…”

“…Librational frequencies increase on cooling, an effect observed previously in experimental and simulated OKE studies on benzene. 70 This is again attributed to the increasing liquid density, where less free space means less free motion of a molecule in a cage, and intermolecular potential landscapes become more quadratic in nature. This also applies to the fast-β mode, where the ω∝ ρ( T ) proportionality also holds.…”

Intramolecular Vibration Energy-Transfer-Driven Cascaded Stimulated Raman Scattering and Four-Wave Mixing in Benzene Series

“…A screen was placed to observe the near-field pattern; a strong central spot that contains the transmitted pump beam and collinear SRS components can be observed. The first-order and cascaded high-order Stokes SRS components were always collinear with the pump beam along the axial direction; some ring-like FWM components with different Stokes and anti-Stokes SRS can also be obtained in the forward direction along different angles apart from the pump beam direction, which usually manifested the conical spatial structure . This type of coherent emission originated from the energy-transfer-enhanced FWM processes.…”

“…To date, most fundamental studies of SRS have been done in a large number of transparent organic solvents, such as benzene, carbon disulfide, nitrobenzene, and carbon tetrachloride. − All above-mentioned liquids generally exhibit a relatively large RSCS and Kerr constant for their vibrational Raman modes and can withstand higher pump intensity to obtain cascaded high-order SRS . The SRS application had made it a focus of research for the last few decades. − Bender et al proposed optical Kerr effect spectroscopy technology by studying the relationship between the Kerr effect of benzene and temperature . He analyzed the FWM in the SRS process of benzene and observed the coherent emission components produced by FWM processes usually manifest conical shaped spatial structures and can be observed only in the forward direction .…”

“…19−23 Bender et al proposed optical Kerr effect spectroscopy technology by studying the relationship between the Kerr effect of benzene and temperature. 19 He analyzed the FWM in the SRS process of benzene and observed the coherent emission components produced by FWM processes usually manifest conical shaped spatial structures and can be observed only in the forward direction. 20 Kakinuma had investigated the low-frequency dynamics of six-membered ring molecular liquids to elucidate the effects of aromaticity on the lowfrequency spectra and ultrafast molecular dynamics.…”