Experimental investigation of the ionization dynamics in slow p–H 2 collisions F. Afaneh a, * ,R.Do ¨rner b , L.Ph.H. Schmidt b , H. Schmidt-Bo ¨cking b a Department of Physics, The Hashemite University, P.O. Box 150459, Zarqa 13115, Jordan b Institut fu ¨r Kernphysik, August-Euler-Straße 6, 60486 Frankfurt am Main, Germany Received 24 October 2004; received in revised form 6 February 2005 Available online 2 June 2005 Abstract The single ionization (SI) and the transfer ionization (TI) of H 2 have been investigated utilizing the Cold Target Recoil Ion Momentum Spectroscopy (COLTRIMS) reaction microscope. Continuum electron velocity spectra have beenmeasuredforexperimentallydeterminednuclearmotion.ElectronvelocitydistributionsfortheSIofH 2 showthat theejectedelectronsliemainlyinthescatteringplanewheretheirvelocitieswerefoundtoliebetweenthoseoftherecoil- ingtargetandthescatteredprojectile.InadditiontoagroupofelectronsseeninSIsaddleelectronsgroup,theelectron velocity spectra for TI of H 2 unveiled the existence of another group of electrons with different structure. These elec- tronswereemittedwithvelocitiesgreaterthantheprojectilevelocityandfoundtoresultfromanarrowrangeofimpact parameters. These fast forward electrons reveal a substantial amount of out-of-plane scattering. Ó 2005 Elsevier B.V. All rights reserved. PACS: 34.50.Gb; 34.70.+e; 39.30.+w 1. Introduction Amajorprobleminmolecularphysicsisioniza- tioninion–moleculecollisions.Thecontinuumdis- tribution of electrons ejected in such collisions is still not completely understood particularly at impact velocities where the collision dynamics possess a molecular character. In slow collisions the electronic wavefunction has time to adjust adiabatically to the slowly changing two-center potential of the target and projectile forming an intermediate quasi-molecule. On rupture of this quasi-molecule the electrons relax in most cases intoboundstatesofeitherthetargetortheprojec- tile. In a few cases, however, one electron is promotedtothecontinuum,leadingtoionization. 0168-583X/$ - see front matter Ó 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2005.02.028 * Corresponding author. Present address: P.O. Box 330039, Zarqa 13133, Jordan. Tel.: +962 795576035; fax: +962 5 3826613. E-mail addresses: afaneh@hu.edu.jo, afaneh@hsb.uni- frankfurt.de (F. Afaneh). Nuclear Instruments and Methods in Physics Research B 234 (2005) 431–440 www.elsevier.com/locate/nimb