Intensity and lifetimes of ZEKE spectra

The questions addressed in this Letter are whether the lifetime or intensity of long-lived molecular ZEKE/Rydberg states are influenced by the intensity of background ions and hence whether these background ions are mechanistically involved in the formation of ZEKE states. We performed an experiment changing the ion density which had no appreciable effect on the intensity of the ZEKE signal. ZEKE states with a lifetime of many tens of microseconds are here not changed by background ions, either in lifetime or intensity.