Electron induced dissociation in the condensed-phase nitromethane: II. Desorption of neurtral fragments

Bazin, M.; Ptasinka, S.; Bass, A. D; Sanche, L.; Burean, E. and Swiderek, P. (2010). Electron induced dissociation in the condensed-phase nitromethane: II. Desorption of neurtral fragments. Journal of Physics: Condensed Matter, 22(8) pp. 1–9.

DOI: https://doi.org/10.1088/0953-8984/22/8/084003

Abstract

Low energy electron induced dissociation in multilayer films of nitromethane (CD₃NO₂) was investigated by high resolution electron energy loss spectroscopy (HREELS) and by the electron stimulated desorption (ESD) of neutral species. HREELS measurements show that the lowest electronic states of the condensed molecule are very similar to those seen in the gas phase. Desorbed neutrals were detected using combined non-resonant multi-photon ionization at 355 nm and time of flight mass spectrometry. The most intense signals detected were those of CD₃ + and NO + and are attributed primarily to the desorption of CD₃ and NO₂ fragments following molecular dissociation via low-lying electronic excited states of nitromethane (the detected NO + being the result of the dissociative ionization of NO₂). By varying the time delay between the incident electron pulse and the ionizing laser pulse, it is possible to measure the kinetic energy distributions of desorbing fragments. The kinetic energy distributions above ~ 5 eV appear invariant with incident electron energy, indicating that the same desorption process (dissociation via low-lying electronic states) operates at all the studied incident energies. Nevertheless, measurements of neutral yields as functions of incident electron energy demonstrate that excitation of the dissociative electronic states also proceeds via previously identified transient negative ions. At energies less than ~ 5 eV, contributions from dissociative electron attachment are also observed in the yield of CD₃ and other neutral fragments.