GASEOUS PHOSPHORUS COMPOUNDS .3. MASS SPECTROMETRIC STUDY OF REACTION BETWEEN DIATOMIC NITROGEN AND PHOSPHORUS VAPOR AND DISSOCIATION ENERGY OF PHOSPHORUS MONONITRIDE AND DIATOMIC PHOSPHORUS

The gaseous equilibria between N2, P, P2, and PN have been studied by means of the Knudsen effusion technique combined with mass spectrometric analysis of the vapor above a condensed UP-BN mixture. The dissociation energy of the P2 molecule has been obtained from the measurement of the equilibrium P2(g) = 2P(g) as D°298 = 117.0 ± 2.5 kcal/mol. The corresponding D°0 value is 116.1 ± 2.5 kcal/mol or 5.04 ± 0.11 eV. The dissociation energy of the PN molecule, D°298 = 147.5 ± 5.0 kcal/mol has been calculated from the measured enthalpies of the reactions P2(g) + N2(g) = 2PN(g) and 2P(g) + N2(g) = 2PN(g) and from pertinent literature values for P2 and N2. The corresponding D°0 value is 146.6 ± 5.0 kcal/mol or 6.4 ± 0.2 eV. The standard heat of formation of gaseous PN, ΔHf°, was derived as 45.3 ± 4.0 kcal/mol.