Medium effects on valence and low‐n Rydberg states: NO in argon and krypton

Absorption and total fluorescence spectra of NO transitions perturbed by argon and krypton at various densities from the dilute gas to the low temperature solid are reported for photon energies 6≤hν≤9 eV. The valence transitions shift monotonically to lower photon energies with increasing perturber number density. The Rydberg transitions to n=3 (A 2Σ+, C 2Π, D 2Σ+) exhibit a moderate red shift at low perturber densities followed by an increasing blue shift with increasing density. Both valence and Rydberg transition energies vary smoothly and continuously with perturber number density even upon the liquid–solid phase transition. For fluid argon the experimental energy shifts are analyzed employing the semiclassical theory for line broadening