  The absorption of infrared and visible radiation from stellar emission
spectra by the negatively charged hydrogen ions H$^{-}$ is considered. We
derive the explicit formulas for the bound-free absorption coefficient
$a_{\nu}$ for the negatively charged hydrogen ion ${}^{\infty}$H$^{-}$ and its
isotopes ${}^{1}$H$^{-}$ (protium) and ${}^{2}$H$^{-}$ (deuterium or D$^{-}$).
The bound-free absorption coefficient $a_{\nu}$ is used to evaluate the actual
absorption of infrared and visible radiation by the H$^{-}$ ion in photospheres
of many cold stars with surface temperatures $T_s \le$ 8,250 $K$.
