Broadening of Highly Excited Atomic Levels in an Atmosphere of Alkali-Metal Atoms

Interactions between a highly excited atom and another atom in the ground state with nonzero electron affinity lead to a splitting of highly excited levels. This situation provides a mechanism which modifies spectral lines of a Rydberg series. Electronic transitions between components of the quasi molecular level due to interatomic motion are analyzed on the basis of the adiabatic theory. The width of a spectral line near the edge of the series is expressed in terms of the electron affinity of the perturbing atom and other calculable quantities. Comparison of the present theoretical result and experimental data for K and Cs shows that this mechanism is as significant for linewidths as the Fermi process for line shifts.