VIBRATIONAL FREQUENCIES AND IDEAL-GAS HEAT-CAPACITIES AS CALCULATED BY A MODIFIED UREY-BRADLEY FORCE-FIELD - FLUOROCHLORODERIVATIVES OF METHANE

Ideal-gas heat capacities are required to estimate caloric properties of fluids. Relationships between ideal-gas and molecular properties ar e given by statistical thermodynamics. For many molecules the required molecular data, i.e. vibrational frequencies, or heat capacity data f rom different references are contradictory or still lacking. Here a me thod is applied, which is able to predict the vibrational frequencies for many molecules from known data of few molecules with an accuracy s ufficient for the calculation of heat capacities. A brief description of the method, based on a mechanical model of the molecules, is given. The application to all fluorochloro-substituted methanes will demonst rate its reliability. Reliable experimental heat capacity data indicat e, that an accuracy of +/-0.8% is achieved. (C) 1997 Elsevier Science B.V.