High-Resolution Spectroscopy of High Rydberg States: Chemical and Technological Applications

Abstract

High Rydberg states of atoms and molecules possess unusual properties that can be exploited in chemistry and technology. The extreme sensitivity of these states to external influences makes them ideal probes of their environment and they can be used to measure electric fields and ion concentrations in the gas phase with high accuracy. The highest Rydberg states with principal quantum number n ≥ 200 lie energetically so close to successive ionization thresholds in atoms and molecules that they can be used to determine ionization potentials precisely and to extract detailed information on the energy level structure of molecular cations. To investigate and better exploit the properties of high Rydberg states, we have developed new high-resolution vacuum ultraviolet laser sources and combined these with millimetre waves in double-resonance experiments. In these experiments a spectral resolution of up to 60 kHz can be achieved. High-resolution spectroscopy is ideally suited to study the fascinating behaviour of high Rydberg states and opens the way to promising applications in the gas-phase chemistry of unstable and charged particles and in measurement technology.