Charge separation in core excited argon clusters is reported. Neutral argon clusters have been prepared in a supersonic molecular beam. Photoionization with monochromatized synchrotron radiation in the L3/L2 regime (240–260 eV) initiates various single and double ionization processes. The photoion–photoion-coincidence (PIPICO) technique is applied to measure dissociative double ionization processes in core excited argon clusters. Three series of charge separation channels are observed: (i) Ar+/Ar+n, (ii) Ar+2/Ar+n, and (iii) Ar+3/Ar+n. Kinetic energy releases from charge separation reactions as well as the relative intensities of the PIPICO signals are discussed in relation to fragmentation mechanisms, resonant Auger spectra, and properties of cluster dications, such as cluster dication fragmentation energies and charge separation distances.

We have studied negative ion formation following low-energy electron impact (0-10 eV) to OClO including a time-of-flight analysis of the ions. The dominant feature is formation of a transient negative ion (OClO − * ) by resonant electron capture in the vicinity of 0.7 eV which decomposes into Cl − , O − , ClO − and O − 2 . The total dissociative attachment (DA) cross section at the resonance maximum (0.7 eV) is near 10 −15 cm 2 with ClO − +O the dominant channel. Although the DA reaction O 2 + Cl − is exothermic by nearly 4 eV the Cl − ion appears with a mean kinetic energy of only 0.4 ± 0.1 eV indicating effective vibrational excitation of neutral O 2 . Also observed at higher target gas pressures is the parent anion ClO − 2 which arises from an effective charge transfer process involving a metastable complex formed in the collision between the dominant DA product ClO − and the sample molecule OClO. Possible implications of these results for the heterogeneous chemistry of OClO on polar stratospheric cloud particles are considered.

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Core level excitation of weakly bonded atomic and molecular species is reported. Excitations into unoccupied orbitals with valence or Rydberg character as well as into the corresponding K-and L-continua are compared with the isolated and condensed species. Core level excitation of clusters is also accompanied with extensive fragmentation of singly and doubly charged clusters. Coincidence techniques such as photoelectronphotoion-coincidences (PEPICO) and photoion-photoion-coincidences (PIPICO) are used to study the photochemical fragmentation pathways of core excited clusters. Kinetic energy releases related to charge separation of cluster dications (Coulomb explosion) are derived from PIPICO spectra. The fragmentation energetics is discussed in relation to cluster dication threshold energies.