Mass spectrometric determination of dissociation energies of high-temperature molecules: ScS, YS, LaS, ZrS, UO

Gaseous isomolecular equilibria of types MS + N = NS + M and MO + N = NO + M, where M and N are variously the elements Sc, Y, La, Zr, and U, were studied mass spectrometrically, over appropriate mixed solid phases heated in a tungsten Knudsen cell. Dissociation energies were derived, using as reference values D/sub 0//sup 0/(US) = 124.0 +- 2.3, D/sub 0//sup 0/(YS) = 125.4 +- 2.5, and D/sub 0//sup 0/(YO) = 170.0 +- 3.0 kcal/mole. ''Preferred values'' obtained by considering the results of the present study and literature values are ScS, 113.4 +- 3.0; YS, 125.4 +- 2.5; LaS, 136.0 +- 3.0; ZrS, 136.6 +- 4.0; and UO, 181.0 +- 4.0 kcal/mole. Determination of ground state degeneracies of US and UO by calculating the electronic entropies of the molecules was attempted. 4 tables, 33 references.