Estimation of gas-phase heat capacities for hydrofluoroethers with two carbon atoms

Density functional calculations at the B3LYP/6-31g* level of theory are used to predict gas-phase heat capacities as a function of temperature for the two-carbon hydrofluoroethers and dimethyl ether. We use equilibrium thermodynamic calculations to determine weighting factors for different rotameric forms to find an observable heat capacity estimate. Hindered rotor corrections were made to the partition functions for these weightings and for the heat capacity contributions for the modes where the harmonic oscillator approximation was inappropriate. We find close agreement with experimental values for the two hydrofluoroethers where heat capacities have been measured and good agreement over a wide temperature range for dimethyl ether. This agreement indicates that the heat capacities we report for the other seven species are accurate and would represent experimental data if it were available in the open literature. This work populates a needed database for the evaluation of these materials as heat transfer media in the temperature range from 100 to 3000 K.