Thermodynamic stability of Sn-4, Sn-5, Sn-6, and Sn-7 clusters by Knudsen cell mass spectrometry

The Knudsen cell mass spectrometric method has been employed to measure the partial pressures of Sn-n (n=1-7) under equilibrium conditions above liqui d tin or a tin-gold alloy, contained in a graphite Knudsen cell. From the a ll-gas analyzed equilibria the following atomization enthalpies Delta(a)H(0 )(:)(Sn-n), and enthalpies of formation, Delta(f)H(298.15)degrees(:)(Sn-n), in kJ mol(-1), have been obtained: Sn-4, 750.2 +/- 14 and 450.6 +/- 14; Sn -5, 990.2 +/- 22 and 512.3 +/- 22; Sn-6, 1349.7 +/- 28 and 452.8 +/- 28; Sn -7, 1644.2 +/- 37 and 460.0 +/- 37. The atomization energies are compared w ith available theoretical values. (C) 2000 American Institute of Physics. [ S0021-9606(00)02029-8].