Radiation and Thermodynamic Characteristics of Hydrogen Gas Near the State of Thermalization

The thermodynamic characteristics of hydrogen gas during the transition from optically thin at line frequencies to a state of thermalization without external radiation sources are studied. The radiative terms in the stationary equations describing discrete transitions between atomic levels are included in the Sobolev approximation. It is shown that the transition to a state of thermalization with an increase in the optical thickness of the gas at the frequencies of spectral lines can be accompanied by a strong (by almost a factor of 100) increase in the degree of ionization of the gas. Electron-impact ionization from excited levels predominates in this process.