High-resolution spectroscopy of high Rydberg states - Chemical and technological applications

High Rydberg states of atoms and molecules possess unusual properties that can be exploited in chemistry and technology. The extreme sensitivity of th ese states to external influences makes them ideal probes of their environm ent and they can be used to measure electric fields and ion concentrations in the gas phase with high accuracy. The highest Rydberg states with princi pal quantum number n greater than or equal to 200 lie energetical ly so clo se to successive ionization thresholds in atoms and molecules that they can be used to determine ionization potentials precisely and to extract detail ed information on the energy level structure of molecular cations. To inves tigate and better exploit the properties of high Rydberg states, we have de veloped new high-resolution vacuum ultraviolet laser sources and combined t hese with millimetre waves in double-resonance experiments. In these experi ments a spectral resolution of up to 60 kHz can be achieved. High-resolutio n spectroscopy is ideally suited to study the fascinating behaviour of high Rydberg states and opens the way to promising applications in the gas-phas e chemistry of unstable and charged particles and in measurement technology .