Thermodynamic properties of solid sulfuryl fluoride

Abstract

The heat capacity of solid sulfuryl fluoride, SO2F2, has been measured over the range 2<T<21 K and in the region of melting with an estimated precision varying between ±1% at the higher temperatures and ±2% at T<5 K. The results agree with those of earlier measurements available above 12 K to within ±1%. However, below 12 K, they significantly affect the values of the residual entropy of SO2F2 based on an extrapolation carried out by Bockhoff et al. [F. J. Bockhoff, R. V. Petrella, and E. L. Pace, J. Chem. Phys. 32, 799 (1960); F. J. Bockhoff and E. L. Pace, J. Chem. Phys. 36, 3502 (1962)]. Analysis of the data indicates that a Schottky anomaly is not present down to 2 K but between 3<T<8 K there is an important contribution to the heat capacity besides that of the lattice vibrations. ΘD(T) curves have been constructed based on different sizes of vibrational unit which allows the coarse features of the lattice frequency spectrum to be determined. The main conclusion reached is that the three components of the spectrum due to translational and rotational vibrations of the SO2F2 molecule and to the intramolecular vibrations are separated. The contribution of the librational modes to the heat capacity can be approximated by a single frequency of 80 cm−1.