Eur. Phys. J. D (2012) 66: 53
https://doi.org/10.1140/epjd/e2012-20670-y

Regular Article

Reactions and anion desorption induced by low-energy electron exposure of condensed acetonitrile

¹ Département de Médecine Nucléaire et Radiobiologie, Faculté de Médecine, Université de Sherbrooke, Sherbrooke, QC, J1H 5N4, Canada
² Universität Bremen, Institut für Angewandte und Physikalische Chemie, Fachbereich 2 (Chemie/Biologie), Leobener Straße/NW 2, Postfach 330440, 28334 Bremen, Germany

^a e-mail: swiderek@uni-bremen.de

Received: 18 November 2011
Received in final form: 11 January 2012
Published online: 28 February 2012

Abstract

Thermal desorption spectrometry (TDS) and electron stimulated desorption (ESD) are employed to investigate mechanisms responsible for the formation of C₂H₆ in electron irradiated multilayer films of acetonitrile (CH₃CN) at 30 K. Using a high sensitivity time-of-flight mass spectrometer, we observe the ESD of anionic fragments H⁻, CH₂^-, CH₃^- and CN⁻. Desorption occurs following dissociative electron attachment (DEA) via several negative ion resonances in the 6 to 14 eV energy range and correlates well with a “resonant” structure seen in the TDS yield of C₂H₆ (i.e., at mass 30 amu). It is proposed that C₂H₆ is formed by the reactions of CH₃ radicals generated following DEA to CH₃CN which also yields CN⁻. Between 2 and 5 eV, a second resonant feature is seen in the C₂H₆ signal. While DEA is observed in the gas phase at these energies, no anion desorption occurs since anionic fragments likely have insufficient kinetic energy to desorb. Since the CH₂^- ion has not been observed in gas-phase measurements, we propose that it is formed, along with HCN (that is detected in TDS) when dissociation into CH₃^- and CN is hindered by adjacent molecules.