Absorption of Microwaves by Oxygen in the Millimeter Wavelength Region

Abstract

Pressure broadening of the absorption lines near 60 000 Mc/sec because of the oxygen molecule has been examined in pure oxygen, and in oxygen-nitrogen mixtures. The apparatus consisted of a large nonresonant cavity spectrometer, with bolometer detectors. At pressures of a few millimeters, a fairly constant ($\frac{\Delta \nu }{P}$) value of 1.94±5 percent (Mc/sec) per mm Hg has been found for pure oxygen, independent of the rotational state of the molecule. To explain absorption in dry air at pressures from one-quarter to one atmosphere, a value of 0.75 for the broadening ratio of ($\frac{\Delta \nu }{P}$) for ${\mathrm{O}}_2$-${\mathrm{N}}_2$ to ($\frac{\Delta \nu }{P}$) for ${\mathrm{O}}_2$-${\mathrm{O}}_2$ accounts satisfactorily for the broadening effect of nitrogen. A theoretical analysis has been applied assuming the important molecular interactions are the London dispersion (polarizability) and exchange forces. Dipole-dipole forces are absent, and quadrupole- and magnetic-dipole effects are found to be too weak to be effective.