Production of Cluster Ions by Laser Vaporization
There have been numerous reports of the production of cluster ions by the method of laser vaporization of solid samples, entrainment of the vaporized species in a supersonic molecular beam, and photoionization of the neutral clusters [1–3]. The exact cluster growth mechanism (s) are not completely understood, and the observed cluster ion distribution may depend upon numerous factors including instrumental parameters. Although the laser vaporization/molecular beam/photoionization technique has been successful in the production of high-mass clusters of a wide variety of materials, other methods of cluster production have been used. In particular, carbon cluster ions have been generated directly by particle bombardment and laser vaporization combined with mass spectrometric detection [4–6]. These direct cluster ion production methods have allowed detection of only relatively small carbon cluster ions, [Cn]+ with n<30. The laser/molecular beam method has allowed detection of a bimodal distribution of carbon cluster ions; both the low-mass distribution, n<30, and a high-mass distribution, 30<n<150. The low-mass distribution with the characteristic cluster interval of n=1 is essentially the same in both methods, despite the significant differences in the experimental conditions. To this point, the high-mass carbon cluster ion distribution, with the cluster interval of n=2 and a maximum ion abundance at n=60, has been observed only using a molecular beam.
KeywordsLaser Vaporization Supersonic Molecular Beam Pulse Delay Time Cluster Formation Process Tungsten Cluster
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- 4.R. E. Honig, in Advances in Mass Spectrometry, vol. 2, R. M. Elliot, ed. (Pergamon Press, Oxford, 1963), p. 25.Google Scholar