A MASS-SPECTROMETRIC STUDY OF THE DISSOCIATION OF THE GASEOUS DIATOMIC TELLURIUM MOLECULE

The dissociation equilibrium, Te2(g) = 2Te(g), was evaluated from the partial pressures of Te(g) and Te2(g) over different metal-tellurides (where the metal = Fe, Cr, Ni or Mo). The equilibrium constants, deduced as a function of temperature (820-1285 K), correspond to a range of monomer-to-dimer ratios, i.e. p(Te)/p(Te2) varying from approximately 0.02 to 1. They are consistent with the available results corresponding to higher temperatures (1195-1467 K), and therefore, the two sets of data were combined into the following dissociation constant-temperature relation (820-1467 K): log(K(dis)degrees/Pa) = [(-13837 +/- 91)/(T/K)] + (11.011 +/- 0.090). The resulting third-law dissociation enthalpy of Te2(g), 257.6 +/- 4.1 kJ mol-1, which we recommend, is in excellent agreement with photoionization or spectroscopic results. The pressure-independent reaction. Te(g) + Te (in condensed phase) = Te2(g) was also evaluated and the following relation was obtained: log K-degrees = [(3930 +/- 51)/(T/K)] - (0.6678 - 0.0513), (820-1285 K). This evaluation confirmed the mutual consistency of the p(Te) and p(Te2) values employed to deduce the dissociation constant-temperature relation as well as the dissociation energy reported here. Furthermore, a correlation between the monomer-to-dimer ratio in the vapour phase to the activity of tellurium in the condensed phase is brought out.