MASS-SPECTROMETRIC INVESTIGATION OF THE THERMODYNAMIC PROPERTIES OF THE SI-5 MOLECULE

The partial pressures of Si(g) and Si-5(g) over condensed silicon have been determined by Knudsen effusion mass spectrometry. Thermal functi ons for Si-5 have been calculated from recent theoretical results. The values for the atomization enthalpy and the enthalpy of formation for gaseous Si-5 are: Delta H-a,H-0, = 1559 +/- 24 kJ mol(-1) and Delta H -f,H-298,H-15 = 700 +/- 24 kJ mol(-1). The fragmentation energy for Si -5 is determined as 399 kJ mol(-1). Recent theoretical predictions are in good agreement with our experimental results.