A generalized Saha equation which explicitly includes excited atomic states and their interactions is used for calculating the degree of ionization and the effective ionization potential for a dense classical partially ionized hydrogen plasma. The effective ionization potential for each atomic state, characterized by the principal quantum number $n$, is calculated as is the change $\Delta I_n$ of the ionization potential due to different types of particle interactions, i.e., atom-atom, atom-ion, atom-electron, and ion-electron interactions. The effective ionization potential for each state is used for determining $n^{*}$, the maximum admissible principal quantum number for a hydrogen atom in a plasma. It is found that the strongest influence on the effective ionization potential comes from the familiar electron-ion interactions (Debye shielding), and from the less effective but not negligible induced-dipole interactions between atom-ion and atom-electron pairs. The van der Waals interactions of the dispersion-type turn out to be negligible in agreement with earlier work. The changes $\Delta I_n$ are shown to produce corresponding changes in the population of the atomic states which are of the order of ten percent; however, the degree of ionization of the total atom is found to be very insensitive to the $\Delta I_n$, and to vary only one tenth of a percent by order of magnitude.

• Received 27 August 1980

DOI:https://doi.org/10.1103/PhysRevA.23.908