Thermochemical properties of Si2F6 and SiF4 in gas and condensed phases

Abstract

The available data for determining the thermochemical parameters for Si2F6 and SiF4 has been assembled. With this information, the thermochemical functions for Si2F6 and SiF4 have been calculated as ideal gases in the harmonic oscillator approximation. These results are presented in the format of the NIST-JANAF Thermochemical Tables, as well as in the format of the CHEMKIN Thermochemical Database. Using the vapor pressure data, the thermochemical parameters for Si2F6 in the solid phase and SiF4 in both the solid and liquid phases have been calculated. These results are compared with available experimental and calculated data. The earlier results are in good agreement with our results. However, the Si2F6 results were not previously available in the JANAF format, and the results for both species are on a much firmer footing with the new experimental data we used. The anharmonicity constants measured earlier for SiF4 permitted a determination of the effect of anharmonicity on the thermochemical properties for this species. For this species at least, the harmonic oscillator approximation is very good. Differences between the harmonic and anharmonic calculations were only significant at temperatures above 1000 K. © 2007 American Institute of Physics.