MASS-SPECTROMETRIC INVESTIGATION OF THE EVAPORATION PROPERTIES OF LEAD-OXIDE

Partial pressures of molecular species over solid PbO were measured in the temperature interval between 890 K and 1100 K using Knudsen-cell mass spectrometry. The assignment of ions is discussed in detail. Stru ctural and vibrational parameters of the gas phase for (PbnOn) (n = 1, 2,3,4) were calculated by the ab initio molecular orbital method at di fferent approximation levels. Third law enthalpies of dissociation of Pb2O2 and Pb4O4 to monomeric PbO were obtained as (250.6 +/- 6) kJ/mol and (835.0 +/- 15) kJ/mol, respectively. The possibility of direct me asurement of the dissociation pressure of PbO by a mass spectrometer I s demonstrated. (C) 1997 by John Wiley & Sons, Ltd.