Collision induced fragmentation of free sulfur clusters

Fragmentation of multiply charged sulfur clusters is investigated by ion-ion-coincidence spectroscopy. The experiments were performed at the electron cyclotron resonance (ECR) ion source at the KVI Groningen, where beams of Xeq+ (q = 5, 10, 15, 20) were produced. The Xeq+ ions were accelerated to kinetic energies of 8-10.q keV and collided with a beam of free sulfur clusters. Variable size sulfur clusters are prepared in a two-stage oven source, where the temperature of the oven was used to adjust the cluster size. Most experiments were performed using S-8, the dominant cluster at low oven temperature. Ion-ion-coincidence as well as mass spectra were recorded. Coincidences between singly charged atomic and molecular fragments were studied, where changes of product channels were observed as a function of charge state of the Xeq+ projectile. The mechanisms of cluster fragmentation are discussed. The results are compared to earlier experiments on core-excited sulfur clusters using soft X-rays. (C) 2008 Elsevier B.V. All rights reserve

Cross sections for energetic heavy-ion impact on protonated water clusters

Energetic impact of multiple ionized oxygen on protonated water clusters in the range of eight to twenty-one water molecules is investigated on the ZERNIKE-LEIF facility. The target water clusters are stored in a Paul trap and thermalized by cold buffer gas. This well-controlled approach allows for a direct measurement of the total inelastic cross section leading to trap-loss processes of the target ions

The electronic structure and deexcitation pathways of an isolated metalloporphyrin ion resolved by metal L-edge spectroscopy

The local electronic structure of the metal-active site and the deexcitation pathways of metalloporphyrins are crucial for numerous applications but difficult to access by commonly employed techniques. Here, we applied near-edge X-ray absorption mass spectrometry and quantum-mechanical restricted active space calculations to investigate the electronic structure of the metal-active site of the isolated cobalt(III) protoporphyrin IX cation (CoPPIX$^+$) and its deexcitation pathways upon resonant absorption at the cobalt L-edge. The experiments were carried out in the gas phase, thus allowing for control over the chemical state and molecular environment of the metalloporphyrin. The obtained mass spectra reveal that resonant excitations of CoPPIX$^+$ at the cobalt L$_33$-edge lead predominantly to the formation of the intact radical dication and doubly charged fragments through losses of charged and neutral side chains from the macrocycle. The comparison between experiment and theory shows that CoPPIX$^+$ is in a $^3$A$_{2g}$ triplet ground state and that competing excitations to metal-centred non-bonding and antibonding σ* molecular orbitals lead to distinct deexcitation pathways