A Mass Spectrometric Study of Phosphorus Oxide

Phosphorus pentoxide has been investigated with a mass spectrometer over the temperature range from 60°C to 650°C. A Knudsen cell has been installed in the source of the mass spectrometer. Two samples were used in the experiment. One was commercially-available phosphorus pentoxide, while the other had been purified from the commercial phosphorus pentoxide by Finch’s method. The ionization efficiency curves near the appearance potential of P4O9+ and P4O10+, the fractional yield of each ion versus the ionizing voltage have been investigated and interpreted as evidence for the presence of the P4O9 molecule. Three curves representing the intensity of the mass 284 (P4O10+) peak as a function of the temperature have been obtained. Two of them, which set on at about 250°C and 450°C respectively, are related to the known vapor pressure curves of phosphorus pentoxide. The curve with the lowest onset temperature, about 100°C, may be interpreted as a vapor pressure of a new low temperature phase of phosphorus pentoxide.