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Water cluster fragmentation probed by pickup experiments
J. Cuvellier, P. Meynadier, P. De Pujo, O. Sublemontier, J. P. Visticot, J. Berlande, A. Lallement, and J. M. Mestdagh, Z. Phys. D 21, 265–269 (1991).
Pick-up is obviously an inelastic process. Momentum transfer has also been used in elastic crossed-beam scattering experiments as a tool for size selection of small neutral clusters. This approach was introduced in Ref. 15 and exploited in numerous publications, including the aforementioned Ref. 7.
J. Lengyel, J. Kočišek, V. Poterya, A. Pysanenko, P. Svrčková, M. Fárník, D. K. Zaouris, and J. Fedor, J. Chem. Phys. 137, 034304 (2012).
H. Pauly, Atom, Molecule and Cluster Beams I: Basic Theory, Production and Detection of Thermal Energy Beams (Springer, Berlin, 2000), Sec. 2.4.1.
H. Pauly, Atom, Molecule and Cluster Beams I: Basic Theory, Production and Detection of Thermal Energy Beams (Springer, Berlin, 2000), Sec. 3.6.2.
N. G. Guggemos, Ph.D. dissertation (University of Southern California, Los Angeles,2014).
The average speed of gas molecules effusing from a long capillary is shifted upwards from this Maxwell-Boltzmann distribution value but not significantly for the present estimate.24
The plotted beam velocities include an estimated correction for the ion flight time within the mass spectrometer, ranging from 2.5% to 5% for the ion masses in the studied range. Adding this correction does not lead to a qualitative change in the entries in Table I and in the conclusions.31
C. Huang, Ph.D. dissertation (University of Southern California, Los Angeles, 2016).
The estimate is guided by the n≈m diagonal in the tables, which may be a plausible assumption.
W. A. de Heer, Ph.D. dissertation (University of California, Berkeley, 1985).
P. Lohbrandt, R. Galonska, H. J. Kim, M. S. C. Lauenstein, and U. Buck, in Atomic and Molecular Beams: The State of the Art 2000, edited by R. Campargue (Springer, Berlin, 2001).
K. Hansen, Statistical Physics of Nanoparticles in the Gas Phase (Springer, Berlin, 2013).
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Electron ionization is a common tool for the mass spectrometry of atomic and molecular clusters. Any cluster can be ionized efficiently by sufficiently energetic electrons, but concomitant fragmentation can seriously obstruct the goal of size-resolved detection. We present a new general method to assess the original neutral population of the cluster beam. Clusters undergo a sticking collision with a molecule from a crossed beam, and the velocities of neat and doped cluster ion peaks are measured and compared. By making use of longitudinal momentum conservation, one can reconstruct the sizes of the neutral precursors. Here this method is applied to H2O and D2O clusters in the detected ion size range of 3-10. It is found that water clusters do fragment significantly upon electron impact: the deduced neutral precursor size is ∼3-5 times larger than the observed cluster ions. This conclusion agrees with beam size characterization by another experimental technique: photoionization after Na-doping. Abundant post-ionization fragmentation of water clusters must therefore be an important factor in the interpretation of experimental data; interestingly, there is at present no detailed microscopic understanding of the underlying fragmentation dynamics.
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