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. HREELSmeasurements show that the lowest electronic states of the condensed moleculeare very similar to those seen in the gas phase. Desorbed neutrals were detectedusing combined non-resonant multi-photon ionization at 355 nm and time offlight mass spectrometry. The most intense signals detected were those ofCD3 + andNO + and are attributed primarily to the desorption ofCD3 andNO2 fragmentsfollowing molecular dissociation via low-lying electronic excited states of nitromethane (the detectedNO + being the result of the dissociative ionization ofNO2). By varying the time delay between the incident electron pulse andthe ionizing laser pulse, it is possible to measure the kinetic energydistributions of desorbing fragments. The kinetic energy distributions above ∼ 5 eV appear invariant with incident electron energy, indicating that the same desorptionprocess (dissociation via low-lying electronic states) operates at all the studied incidentenergies. Nevertheless, measurements of neutral yields as functions of incidentelectron energy demonstrate that excitation of the dissociative electronic states alsoproceeds via previously identified transient negative ions. At energies less than ∼ 5 eV, contributions from dissociative electron attachment are also observed in the yield ofCD3 and other neutral fragments.
Published Version
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