Inverse laser ablation: Formation and chemistry of nanoparticles from gaseous precursors

Unlike traditional laser ablation experiments where solids are volatilized by the focused laser beam, we give the term 'inverse laser ablation' to the process of particle formation following the interaction of the laser with a gaseous precursor. Experiments are described where the transition from a normally gas phase species to a normally condensed phase particle takes place within a single gas-phase cluster in a collisionless environment. In addition, by adding reactant molecules to the initial cluster, it is possible to observe and characterize chemical reactions occurring within this novel 'test tube'. In this technique, a heterocluster composed of iron pentacarbonyl molecules and potential reactant species is formed by coexpansion in a supersonic jet. Photoionization of the precursor molecules by a picosecond, 266 nm laser pulse efficiently strips away the ligands, leaving metal ions and metal cluster ions (and neutrals) in close proximity to reactant molecules. Subsequent reactions take place which are followed by monitoring the products by time-of-flight mass spectrometry. The reaction with carbon disulfide is described in detail.