Spectroscopic and acoustic studies on the internal rotation in 1,2-di-bromo-1,1,2,2-tetrafluoroethane

Abstract

The enthalpy difference and potential-energy barrier to rotation in liquid 1,2-dibromo-1,1,2,2-tetrafluoroethane have been found from spectroscopic and ultrasonic measurements. Comparison of enthalpy differences determined by these two techniques shows that the assumption, (ΔV°/V)(C_p/θ)ΔH°, used in ultrasonic theory to evaluate enthalpy differences is not justified (ΔV° is the volume change in total molar volume V, ΔH° the enthalpy difference, C_p the specific heat at constant pressure, and θ the coefficient of thermal expansion). The potential barriers found by the two techniques agree to within the expected accuracy.