A high intensity cluster ion source for fast beam experiments

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Abstract
A high intensity cluster ion source that can be used for various fast beamspectroscopic studies has been constructed and demonstrated. The cluster ions are grown around seed ions that are generated by electron impact ionization of gas very near the exit of the nozzle (∼1 nozzle diameter distance). The generated cluster ions are coaxially focused and extracted from the pulsed (10 Hz, 200 μs pulse) supersonic expansion through a skimmer by applying a weak (∼1 V/cm) electric field, and injected into a photofragment spectrometer. With the source we have successfully generated well‐collimated intense beams of various positive and negative cluster ions, such as H+ n , H3O+■ (H2) n , (CO)+ n , (N2)+ n , (CO2)+ n , (NO)+ n , He+ n , Ar+ n , Xe+ n , and (CO2)− n , with peaks currents of ∼500 pA at cluster size n=10. Preliminary photofragmentation studies of selected cluster ions have been performed to demonstrate the capability of the source.