Study of electronic states and geometry of size-selected clusters by means of an electron-ion multiple coincidence spectroscopy

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A cluster generation system was made in order to produce rare gas clusters efficiently. This system was mounted on an electron-ion multiple coincidence apparatus and de-excitation mechanism of size-selected clusters was investigated.Interatomic Coulombic decay (ICD) from an Auger-final dicationic state is observed in the Ar dimer. A 2p inner-shell vacancy created by photoionization is replaced with 3s and 3p vacancies via intra-atomic Auger decay. The Auger-final dicationic state is subject to ICD in which one of the 3p electrons in the same Ar atom fills the 3s vacancy while one of the 3p electrons from the neighboring Ar atom is emitted as an ICD electron. This ICD process is unambiguously identified by electron-ion-ion coincidence spectroscopy in which the kinetic energy of the ICD electron and the kinetic energy release between Ar^+ and Ar^<2+> are measured in coincidence.Auger electron spectra recorded in coincidence with two Ar^+ ions produced from Ar_2^<2+> suggest that the bound one-site two-hole state, Ar^<2+>(3p^<-2>)-Ar, decays further only via radiative charge transfer to the dissociative two-site two-hole states Ar^+(3P^<-1>)-Ar^+(3p^<-1>) The measured kinetic energy release of Ar_2^<2+> agrees well with the theoretical estimate based on this process.