Thermodynamic study of small silicon carbide clusters with a mass spectrometer

The Knudsen effusion mass spectrometric method has been used to measure the equilibrium partial pressures of SiC2, Si2C, Si2C2, and Si3C above the SiC-graphite system at temperatures between 1750 and 2000 K. New thermal functions have been calculated for these molecules from recent literature experimental and theoretical molecular parameters and combined with the measured partial pressures to obtain the atomization enthalpies, Delta H-a,H-0, in kJ mol(-1): 1247 +/- 8 (SiC2), 1052 +/- 10 (Si2C), 1652 +/- 14 (Si2C2), and 1437 +/- 14 (Si3C). The derived enthalpies of formation, Delta H-f,H-298, in kJ mol(-1), are 633 +/- 9 (SiC2), 566 +/- 11 (Si2C), 678 +/- 15 (Si2C2), and 632 +/- 15 (Si3C).