title: Lorentz-Lorenz coefficient, critical point constants, and coexistence curve of 1,1-difluoroethylene.
abstract: We report measurements of the Lorentz-Lorenz coefficient density dependence L(rho), the critical temperature Tc, and the critical density rho c of the fluid 1,1-difluoroethylene H2C2F2. Lorentz-Lorenz coefficient data were obtained by measuring refractive index n, and density rho of the same fluid sample independently of one another. Accurate determination of the Lorentz-Lorenz coefficient is necessary for the transformation of refractive index data into density data from optics-based experiments on critical phenomena of fluid systems done with different apparatuses, with which independent measurement of n and rho is not possible. Measurements were made along the coexistence curve of the fluid and span the density range 0.01 to 0.80 g cm(-3). The Lorentz-Lorenz coefficient results show a stronger density dependence along the coexistence curve than previously observed in other fluids, with a monotonic decrease from a density of about onward, and an overall variation of about 2.5% in the density range studied. No anomaly in the Lorentz-Lorenz function was observed near the critical density. The critical temperature is measured at Tc=(302.964+/-0.002) K (29.814 degrees C) and the measured critical density is rho c=(0.4195+/-0.0018) g cm(-3).
authors.affiliation: Department of Physics and Astronomy, The University of British Columbia, 6224 Agricultural Road, Vancouver, B.C., Canada V6T 1Z1. fameli@physics.ubc.ca
authors.forename: Nicola
authors.initials: N
authors.lastname: Fameli
authors.forename: David A
authors.initials: DA
authors.lastname: Balzarini