Formation of even-numbered hydrogen cluster cations in ultracold helium droplets.

J Chem Phys

Institut für Ionenphysik und Angewandte Physik, Leopold Franzens Universität, Technikerstr. 25, A-6020 Innsbruck, Austria.

Published: December 2008

AI Article Synopsis

  • Researchers have developed methods to grow neutral hydrogen clusters inside ultracold helium nanodroplets by picking up hydrogen molecules sequentially.
  • Even-numbered hydrogen cluster ions (cations) have been observed when these clusters are ionized by electron impact, alongside the more common odd-numbered hydrogen ions.
  • High-resolution mass spectrometry has been used to accurately identify these even-numbered ions, revealing unique abundance patterns that imply specific structural configurations, with noted drops in abundance at certain cluster sizes.

Article Abstract

Neutral hydrogen clusters are grown in ultracold helium nanodroplets by successive pickup of hydrogen molecules. Even-numbered hydrogen cluster cations are observed upon electron-impact ionization with and without attached helium atoms and in addition to the familiar odd-numbered H(n)(+). The helium matrix affects the fragmentation dynamics that usually lead to the formation of overwhelmingly odd-numbered H(n)(+). The use of high-resolution mass spectrometry allows the unambiguous identification of even-numbered H(n)(+) up to n approximately = 120 by their mass excess that distinguishes them from He(n)(+), mixed He(m)H(n)(+), and background ions. The large range in size of these hydrogen cluster ions is unprecedented, as is the accuracy of their definition. Apart from the previously observed magic number n=6, pronounced drops in the abundance of even-numbered cluster ions are seen at n=30 and 114, which suggest icosahedral shell closures at H(6)(+)(H(2))(12) and H(6)(+)(H(2))(54). Possible isomers of H(6)(+) are identified at the quadratic configuration interaction with inclusion of single and double excitations (QCISD)/aug-cc-pVTZ level of theory.

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Source
http://dx.doi.org/10.1063/1.3035833DOI Listing

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