Figure 2.3.Schematic of the apparatus used to observe silver cluster ion photofragmentation. The pulsed valve at A controls He gas that carries silver, vaporized by an excimer laser near B, through the nozzle and into the source chamber as a molecular beam. This beam is skimmed and the ions in it are extracted by pulsed electric fields at C into a reflectron time of flight mass spectrometer. To photofragment only one size cluster, a mass gate at D that consists of wires normally at a few hundred volts and caged in a shielding metal box, is briefly grounded to permit the passage of the cluster size of interest. After passing through this gate the cluster packet is collimated and irradiated near E with the dissociation laser that passes through the reflecting fields F of the mass spectrometer and end window. Clusters that do not fragment and charged fragments then follow different trajectories within the reflecting field and reach G, the detector, at different times. The fluence of the dissociation laser is monitored with a photodiode placed after attenuating filters at H.