PHOTOIONIZED TOF MASS SPECTROMETRY OF ATOMIC CLUSTERS.

Generation of carbon, silicon, and silver clusters by a laser- vaporization supersonic expansion cluster beam source was studied using a reflectron-type time-of-flight (TOF) mass spectrometer. The atomic cluster was generated by the laser vaporization of a solid sample disk, followed by cooling with supersonic expansion of pulsed helium gas. The neutral cluster, carried by helium gas, was ionized by a fourth harmonic Nd:YAG laser and accelerated by high voltage to the reflectron mass spectrometer. Positi ve-ion TOF mass spectra of carbon, silicon, and silver clusters were compared for se veral cluster source nozzle conditions. Helium gas pressure at the time of vaporization of solid material played the key role in cluster size range obtained. The effect of pressure was thoroughly examined for a relatively large carbon cluster, which was regarded as fullerene. [ABSTRACT FROM AUTHOR]