The Free-Free Absorption Coefficient of the Negative Hydrogen Ion

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Abstract
The 1s, 2s and 2p states of hydrogen have been included in the Hartree–Fock eigenfunction expansion for the continuum wave functions of the proton and two electron system to allow for exchange and distortion effects in the calculation of the free–free absorption coefficients of the negative hydrogen ion. The contributions of both the S ↔ P and P ↔ D angular momentum transitions were determined, showing that the P ↔ D transitions may not be neglected. Use was made of the length and velocity dipole operators and also, in some instances, of an acceleration dipole operator. The most extensive calculations were carried out with the ‘1s−2s’ exchange strong-coupling continuum functions. The best absorption coefficient values obtained are between the earlier results obtained by neglecting exchange and polarization (Chandrasekhar & Breen) and by allowing for these effects with approximate formulae for the absorption matrix elements (Ohmura & Ohmura). The present calculations give results in close agreement with the improved matrix element approximation results of John (1965) and with the values obtained by Geltman (1965) using variationally determined continuum functions.

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