The Measurement of the Vapor Pressure of Atomic Species from Spectrophotometric Measurements of the Absorption of Resonance Lines. I. Test of the Method on the Vapor Pressure of Sodium

摘要

A method was developed for studying the equilibrium vapor pressure of atomic species over refractory ceramics. It consists of measuring the absorption coefficient of the hot equilibrium vapor at the center of an atomic resonance line. A resonance line of known oscillator strength for the atomic species under examination is generated in liquid nitrogen cooled, hollow cathode discharge tube, and the absorption of this line by a known length of equilibrium vapor present in an isothermal cell is measured using spectrophotometric techniques. After correcting for the various causes of line broadening of the resonance line, the measured absorption is used to calculate the density of the atomic species. The experimental and theoretical techniques are described, and the results of a reinvestigation of the vapor pressure of sodium metal at 400K are given. It is shown that the individual vapor pressure measurements have a root mean square deviation of 12%, and that their average differs from the best literature values by less than 3%. The various sources of error are discussed quantitatively, and it is shown that pressure of 10 to the minus 8th power to 10 to the minus 9th power atmospheres of atomic species can be generally measured with an accuracy of = 20%. (Author)