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Articles you may be interested inAtomization enthalpy and enthalpy of formation of gaseous Si4 from mass spectrometric equilibrium measurements J. Chem. Phys. 99, 7998 (1993); 10.1063/1.465676Mass spectrometry of and standard enthalpies of formation of gaseous sodium tetrachloroaluminate and its dimer J. Chem. Phys. 87, 654 (1987); 10.1063/1.453560 Mass spectrometric determination of the heats of formation and atomization energies of the molecules Ge2N and GeSiNRecent experimental and theoretical studies have allowed us to calculate new thermal functions for the Si 2 and Si 3 molecules. We have determined the atomization enthalpies and enthalpies of formation of Si 2 and Si 3 from mass spectrometric data and have combined them with reevaluated previously published mass spectrometric data using a consistent set of ionization cross sections and thermal functions. The selected atomization enthalpy and enthalpy of formation for the Si 2 molecule are ⌬H a,0 ϭ319Ϯ7 and ⌬H f ,0 ϭ584Ϯ7 kJ mol Ϫ1 , the corresponding values for Si 3 are 705Ϯ16 and 649Ϯ16 kJ mol Ϫ1 . Reevaluated values for Si 4 are 1151Ϯ22 and 654Ϯ22 kJ mol Ϫ1 . Experimental literature values ͑Neumark and co-workers͒ for the electron affinities of Si 2 -Si 4 have been combined with the present results to obtain enthalpies of formation and binding energies for the anions Si 2Ϫ -Si 4 Ϫ . The experimental atomization enthalpies are compared to recent theoretical studies.

The Knudsen cell mass spectrometric method has been employed to measure the partial pressures of Sn n (nϭ1-7) under equilibrium conditions above liquid tin or a tin-gold alloy, contained in a graphite Knudsen cell. From the all-gas analyzed equilibria the following atomization enthalpies ⌬ a H 0 ‫ؠ‬ (Sn n), and enthalpies of formation, ⌬ f H 298.15 ‫ؠ‬ (Sn n), in kJ mol Ϫ1 , have been obtained: Sn 4 , 750.2Ϯ14 and 450.6Ϯ14; Sn 5 , 990.2Ϯ22 and 512.3Ϯ22; Sn 6 , 1349.7Ϯ28 and 452.8Ϯ28; Sn 7 , 1644.2Ϯ37 and 460.0Ϯ37. The atomization energies are compared with available theoretical values.

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