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

S. Jaksch, A. Mauracher, A. Bacher, S. Denifl, F. Ferreira da Silva, H. Schöbel, O. Echt, T. D. Märk, M. Probst, D. K. Bohme, P. Scheier
2008 Journal of Chemical Physics  
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
more » ... f even-numbered H n + up to n Х 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 ͑QCISD͒/aug-cc-pVTZ level of theory
doi:10.1063/1.3035833 pmid:19071915 fatcat:5qgqltfrwbflberl6qz6wu6ys4