The absorption of radiation in the free-free transition of the negative hydrogen ion is the inverse process of bremsstrahlung from an electron in the vicinity of a neutral hydrogen atom. This process is the most important cause of continuous absorption by the atmosphere of the sun and stars in the infrared region. The transition matrix element is expressed, with sufficient accuracy, in terms of the $s$ phase shifts of electron-hydrogen atom scattering alone. To meet the requirement in astrophysical studies, the continuous absorption coefficients due to the free-free transition have been tabulated for a wide range of wavelengths (4050 A to infinity) and temperatures (2520 to 10 080°K) of the hydrogen gas, by using the $s$ phase shifts of $e$-H scattering which include exchange and correlation effects between two electrons. The tabulated coefficients are 20-70% less than the ones computed by Chandrasekhar and Breen, who used Hartree functions without exchange. Further improvement of the present result is discussed.

• Received 31 August 1960

DOI:https://doi.org/10.1103/PhysRev.121.513