On the Thermal Activation of the Oxygen Molecule

Abstract

A study of the relative partial pressures of ${\mathrm{O}}_2$ and the impurities C${\mathrm{O}}_2$, CO and ${\mathrm{H}}_2$O upon the temperature of a platinum filament operated in oxygen at low pressure (about ${10}^{-4\mathrm{}}$ mm of mercury) has been made. The platinum filament was contained in the vacuum system of a mass spectrometer which was used as a partial pressure gauge. It was found that the partial pressure of oxygen began to fall at a filament temperature of approximately 1280°K and had dropped to 46 percent of its original value at 1740°K. This fall in the ${\mathrm{O}}_2$ abundance was accompanied by rises in those of C${\mathrm{O}}_2$, CO and ${\mathrm{H}}_2$O. Finally the effect completely disappeared. A number of considerations make it plausible that the process responsible for this effect involves the adsorption on the hot platinum filament of the oxygen molecules which on evaporation in activated form react with substances of low vapor pressure adhering to the glass envelope. The nature of the activation is most probably excitation to the metastable molecular states ${}_{}{}^1{}_{}{}^{}\Delta$ and ${}_{}{}^1{}_{}{}^{}\Sigma$. The dissociation of hydrogen by a hot tungsten filament has also been investigated and results in accord with previous work obtained.