The role of electric fields and ion concentrations in the formation and stabilization of high-n Rydberg states

ZEro Kinetic Energy (ZEKE) spectroscopy relies on electrons produced throug h delayed field ionization of the narrow band of high-n Rydberg states whic h exist just below the ionization limit of each ionic eigenstate. Using the unique properties of these weakly bound, stable, high-n Rydberg slates (ZE KE states) below the ionization limit rather than the unbound states above the limit, as in PES, leads to an improvement in resolution of more than tw o orders of magnitude. Several different types of ZEKE experiments, each de signed to probe the formation and stability of these slates, are presented here. These experiments were performed with pulsed and static electric fiel ds of different magnitude and duration at different ion concentrations. The results indicate an enhanced ZEKE state decay with increasing electric fie ld strengths and an enhanced formation and stabilization with increasing io n concentrations. A strong interplay between held strength and ion concentr ation ZEKE state formation is demonstrated. The strong influence of electri c fields and ion concentrations on the physical properties of the ZEKE slat e, above and below the classical ionization threshold, is also demonstrated through late time (tens of microseconds) decay rate measurements.