Electron induced dissociation in condensed-phase nitromethane I: desorption of ionic fragments

Abstract

Low energy electron induced dissociation of condensed nitromethane was investigated by measuring the electron stimulated desorption of anions and cations from multilayer films of CH₃NO₂ and CD₃NO₂, using a recently constructed, high sensitivity time of flight mass spectrometer. The desorbed yields were measured as a function of incident electron energy in the range between 1 to 20 eV and as function of coverage on Pt and Xe substrates. In anion desorption experiments, the following ions were observed: H⁻ (D⁻), O⁻, OH⁻ (OD⁻), CN⁻, NCO⁻, NO₂⁻, CHNO₂⁻ (CDNO₂⁻), CH₂NO₂⁻ (CD₂NO₂⁻). Resonant structure seen in all anion yield functions, is attributed to dissociative electron attachment (DEA), though certain anion signals [e.g., OH⁻ (OD⁻) and CH₂NO₂⁻ (CD₂NO₂⁻)] are likely the result of reactive scattering by O⁻ ions. The dominant desorbed cation signals are CD₃⁺ and NO⁺, and the appearance potentials of these species were measured to be 12.2 and 11.5 eV, respectively. The present measurements provide information on how the electron-induced dissociation processes of this proto-typical explosive molecule are modulated by the condensed environment and on how initial dissociation events occurring on a particular molecule, may induce further dissociation.