Waves in a partially ionized paramagnetic gas

The nature of electromagnetic wave propagation in a partially ionized paramagnetic gas in a static magnetic field is explored. It is necessary to characterize such a medium by second-order tensor expressions for both the permittivity and permeability, the former being that characteristic of an ordinary magnetoplasma, and the latter that for a magnetized paramagnetic medium. Employing linearized forms of these and Maxwell's equations leads to a general dispersion relation. For lossless conditions it is shown that the resonances and cutoffs associated with the free electrons and those due to the paramagnetic constituents are independent. This leads to some interesting, hypothetical propagation conditions that may exist in planetary or stellar atmospheres. Application of this theory is made to the ionosphere, in which atomic oxygen is the major paramagnetic constituent. Accounting for collisional losses, it is shown that the upper limit of the absorption at the peak of the atomic oxygen electron spin resonance line in the ionosphere is only 5 × 10
⁻⁴
times the background absorption due to the free electrons; the effect of Doppler broadening would be to decrease this number. The minute nature of this absorption line is supported by the apparently complete lack of experimental evidence of electron spin resonance effects on radio wave propagation in the terrestrial ionosphere. It is also shown that the internal radiation (noise) in the ionosphere must exhibit a similarly weak absorption line at the electron spin resonance, due to the nonequilibrium nature of the energy distribution of the free electrons.