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 S8, 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.