The reliability of absorption coefficients for free-free transitions of the negative helium ion

The reliability of current estimates of free-free absorption coefficients of the negative helium ion are assessed. Results by sophisticated versions of the multiconfiguration-self-consistent field, close-coupling and polarized orbital methods are shown to have converged to within a few per cent of each other for wavelengths greater than 1 μm over the temperature range 1400 K to 25 200 K. A table of coefficients giving the best current estimates of He- continuous absorption are presented. (author)