Microwave Absorption in Compressed Oxygen

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Abstract
Precise measurements of the absorption in oxygen resulting from the small magnetic dipole moment are reported at frequencies near 2, 3, 9, and 23 kMc and at pressures in the range from 3 to 70 atmos. Up to 10 atmospheres the resonant contribution agrees with the Van Vleck‐Weisskopf theory and the line width increases in proportion to the pressure. The line width (relaxation frequency) for the nonresonant contribution also increases in proportion to the pressure, but is only about one‐third as large as the resonant line width. Above 20 atmospheres the resonant absorption shows anomalous behavior resembling that previously noted in the case of the inversion spectra of NH3 and ND3. In particular, the resonant frequency appears to decrease rapidly while the line width changes much less rapidly than the pressure.