The Knudsen cell mass spectrometric method has been employed to measure the partial pressures of the Si[sub 7] and Si[sub 8] clusters under equilibrium conditions above liquid silicon, contained in a boron nitride liner inside a graphite Knudsen cell. Gaussian 2 (G2) theory and B3LYP density functional method were employed to determine the geometry, the vibrational frequencies, and the binding energy of the Si[sub 8] cluster. From the all-gas analyzed equilibria the following atomization enthalpies, Δ[sub a]H[sub 0][sup o](Si[sub n]), and enthalpies of formation, Δ[sub f]H[sub 298.15][sup o](Si[sub n]), in kJ mol-1, have been obtained: Si[sub 7], 2381±36 and 743±36; Si[sub 8], 2735±65 and 837±65. Experimental literature values for the electron affinities of Si[sub n](n=3–8) have been combined with present and previous results to obtain the bonding energies for the Si[sub n][sup -](n=3–8) cluster anions. The experimental atomization energies are compared with available theoretical values.
Meloni, G., Gingerich, K. A. Thermodynamic investigation of the Si[sub 7] and Si[sub 8] clusters by Knudsen cell mass spectrometry. Journal of Chemical Physics. 9/22/2001, Vol. 115 Issue 12.