Measurement of Negative Ions Formed by Electron Impact. II. The Ionization Efficiency Curves of Negative Nitro, Oxygen Atom and Nitromethylene Ions from Nitroalkanes

The ionization efficiency (IE) curves of NO2−, O− and CH2NO2− ions from nitroalkanes (nitro-methane, nitroethane, 1-nitropropane and 2-nitropropane) have been measured with a Hitachi RMU-6D mass spectrometer. Based on each authorized value of IP(CH3, C2H5, C3H7, O and H), D(C–NO2, C–H, C–C, NO–O and N–O), EA(NO2 and O) and the excitation energy of CH3, the respective onsets observed for the electron energies above ∼3 eV on the IE curves were suggested to be interpreted as appearance potentials of the following reactions. For NO2− ions, RNO2+e→R*+NO2−, RNO2+e→R+NO2−+e; for O− ions, RNO2+e→RNO+O−, RNO2+e→RN+O+O−, RNO2+e→RN++O+O−+e;for CH2NO2− ions, CH3NO2+e→H+ CH2NO2−+e, RNO2+e→H+R1+CH2NO2−. On the other hand, the strong peak of NO2− ions due to the dissociative electron capture process (RNO2+e→R+NO2−) was observed at the lower electoron energy. Furthermore, a value of EA(CH2NO2) was presented to be ∼0.5 eV.