The influence of the Ramsauer-Townsend effect on free-free absorption coefficients of the negative argon ion at far infrared wavelengths

Ar- free-free absorption coefficients in the far-IR are calculated using relativistic continuum wavefunctions from solutions of the Dirac equation. Absorption coefficients are shown to exhibit a Ramsauer-Townsend minimum near 1200 K. We compare these results with coefficients derived from non-relativistic and experimental atomic data.