Electron-ion multiple coincidence spectroscopy for small molecules and clusters

We have developed an electron-ion multiple coincidence technique at BL27SU at SPring-8 in Japan, which consists of electron and ion time-of-flight analyzers with multi-hit two-dimensional position sensitive detectors and a supersonic jet from a cooled nozzle. Recent studies on the electron-ion multiple coincidence experiments using this apparatus are reviewed in this paper. We discuss N 1s photoelectron angular distributions in the molecular frame for NO using a new projection analysis method. As an example of de-excitation processes, we have observed interatomic Coulombic decay (ICD) from an Auger-final dicationic state with 3s and 3p holes in the Ar trimer. This ICD process is unambiguously identified by the electron-ion-ion-ion coincidence technique in which the kinetic energy of the ICD electron and the kinetic energy release in the three Ar+ fragmentation are measured in coincidence.