Atomization enthalpies and enthalpies of formation of Ge-3 and Ge-4 by Knudsen effusion mass spectrometry

The high-temperature mass spectrometric method was employed to measure the equilibrium partial pressures of Ge-3 and Ge-4 above liquid germanium conta ined in a graphite Knudsen cell. These data were combined with thermal func tions for Ge-3 and Ge-4, calculated from recent theoretical and spectroscop ic molecular parameters, to evaluate the atomization enthalpies and enthalp ies of formation. Mass spectrometric equilibrium data for Ge-3 and Ge-4 ava ilable in literature were also re-evaluated. The following atomization enth alpies, Delta (a)H(0)degrees (Ge-n,g) and enthalpies of formation Delta (f) H(298.15)degrees (Ge-n,g), in kJmol(-1), are overall assessed values: Ge-3, 589.8 +/- 19 and 531.9 +/- 19; Ge-4, 969.4 +/- 24 and 527.7 +/- 24. The at omization energies are in very good agreement with predictions by Deutsch e t al. [Chem. Phys. Lett. 270 (1997) 413] using Gaussian-2 theory. (C) 2000 Elsevier Science B.V. All rights reserved.