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

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.