Atomic and Molecular Low-n Rydberg States in Near Critical Point Fluids

Since electronic excited states are sensitive to the local fluid environment, dopant electronic transitions are an appropriate probe to study the structure of near critical point fluids (i.e., perturbers). In comparison to valence states, Rydberg states are more sensitive to their environment [1]. However, high-n Rydberg states are usually too sensitive to perturber density fluctuations, which makes these individual dopant states impossible to investigate. (Nevertheless, under the assumption that high-n Rydberg state energies behave similarly to the ionization threshold of the dopant, dopant high-n Rydberg state behavior in supercritical fluids can be probed indirectly by studying the energy of the quasi-free electron, through photoinjection [2–11] and field ionization [12–19].) Low-n Rydberg states, on the other hand, are excellent spectroscopic probes to investigate excited state/fluid interactions.