Electron interaction with nitromethane embedded in helium droplets: attachment and ionization measurements

Results of a detailed study on electron interactions with nitromethane (CH3NO2) embedded in helium nanodroplets are reported. Anionic and cationic products formed are analysed by mass spectrometry. When the doped helium droplets are irradiated with low-energy electrons of about 2 eV kinetic energy, exclusively parent cluster anions (CH3NO2)n− are formed. At 8.5 eV, three anion cluster series are observed, i.e., (CH3NO2)n−, [(CH3NO2)n–H]−, and (CH3NO2)nNO2−, the latter being the most abundant. The results obtained for anions are compared with previous electron attachment studies with bare nitromethane and nitromethane condensed on a surface. The cation chemistry (induced by electron ionization of the helium matrix at 70 eV and subsequent charge transfer from He+ to the dopant cluster) is dominated by production of methylated and protonated nitromethane clusters, (CH3NO2)nCH3+ and (CH3NO2)nH+.