Eur. Phys. J. D 43, 117-120 (2007)
https://doi.org/10.1140/epjd/e2007-00093-9

Electron impact ionization of thymine clusters embedded in superfluid helium droplets

¹ Institut für Ionenphysik und Angewandte Physik, Leopold Franzens Universität Innsbruck and Center of Molecular Biosciences Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria
² Université Catholique de Louvain, Département de physique, unité PAMO, Chemin du cyclotron 2, 1348 Louvain-la-Neuve, Belgium
³ Facoltà di Farmacia, Dipartimento di Studi di Chimica e Tecnologia delle Sostanze Biologicamente Attive, Università “La Sapienza”, Rome, Italy
⁴ University of New Hampshire, 131 Main Street Nesmith Hall, Durham, NH, 03824, USA

Corresponding author: ^a fabio.zappa@uibk.ac.at

Received: 24 July 2006
Revised: 10 September 2006
Published online: 24 May 2007

Abstract

Embedding molecules in helium clusters has become a powerful technique for the preparation of cold targets for spectroscopy experiments, as well as for the assembly of complex, fragile molecular species. We have recently developed a helium cluster source and a pick-up cell to produce neutral beams of doped helium droplets, to be used as targets in studies on electron collisions with molecules of biological relevance. In the present work we present the results of a series of experiments on electron-impact ionization of helium clusters doped with thymine and 1-methylthymine, where several interesting phenomena were observed, i.e., (i) electron impact ionization of molecular clusters inside the helium droplets leads predominantly to protonated clusters; (ii) the appearance energies are close to the ionization threshold of the helium atom but ionization efficiency curves in addition extend down by several eV; (iii) ionized molecular clusters can undergo metastable decay via the loss of one neutral monomer.