MASS-SPECTROMETRY INVESTIGATION OF THE STABILITY OF THE GASEOUS CLUSTERS IN EQUILIBRIUM WITH THE METASTABLE VARIETY OMEGA-SULFUR

Mass spectrometry coupled with the Knudsen effusion method has been applied to the study of the evaporation behaviour of the polymeric form S-omega of sulphur. This form is metastable compared with the orthorhombic form S-alpha, whose structure consists of rings of eight atoms. The measurements yield the composition of the vapour phase, the concentration of the different clusters and the thermodynamic data corresponding to the equilibria between the condensed and the gas phase as well as those taking place in the vapour. Owing to the presence of the clusters S-n, the problem of their fragmentation during the ionization process has to be carefully investigated. A preliminary study of the stable form S-alpha allowed the determination of correction coefficients to take into account this effect by comparing the results with those published up to now. The results obtained in this study show that the equilibria between the condensed phase and the gaseous phase are modified by the structure of the condensed phase. Consequently, the relative concentration of the gaseous clusters is influenced by the nature of the condensed phase. The fact that the enthalpies of reaction remain unchanged can be considered as a check that the thermodynamic equilibrium is obtained within the gas phase.