Measurement of Negative Ions Formed by Electron Impact. III. The Ionization Efficiency Curves of Negative Ions of m⁄e 26 and 42 from Nitroalkanes

Abstract

The studies of this series were extended to the negative ions of m⁄e 26 and 42 obtained from nitroalkanes; nitromethane, nitroethane, 1-nitropropane, and 2-nitropropane. For m⁄e 26 (probably, CN−) ions, the contribution of three or two processes in the range from zero to ∼20 eV of electron energy was observed for nitromethane or other samples. On the basis of ΔHf values of the reactants and products, and of the value of EA(CN), the plausible reactions to be assigned to each process were presented. For the first process, CH3NO2+e−→CN−+H2O+OH, RNO2+e−→CN−+R1OH+OH. For the second process, CH3NO2+e−→CN−+H2O+O+H, CH3NO2+e−→CN−+H2+O2+H, RNO2+e−→CN−+R1+HO2+H, and C3H7NO2+e→CN−+C2H4+H2+O+OH irrespective of kind of nitropropane. For the third process, CH3NO2+e−→CN−+3H+O2. For m⁄e 42 (probably, CNO−) ions, the contribution of two processes was observed. By taking ΔHf (CNO)=x (eV), EA(CNO)=y (eV), and also combining the observed onset values with the calculated values of appearance potential of reactions to be assigned for each process — for the first process, CH3NO2+e→CNO−+H2+OH, RNO2+e−→CNO−+R1OH+H; for the second process, CH3NO2+e−→CNO−+HO+2H, CH3NO2+e−→CNO−+H2+O+H, RNO2+e−→CNO−+R1O+2H– a relation of x−y\simeq2(eV) was derived.

Gas-phase clustering reactions of NO2−, C2H3NO2−, C2H4NO2−, C2H5NO2− and C2H5NO4− with C2H5NO2

“…The C 2 H 5 NO 2 − ion is not observed as an isolated compound under collision-free conditions [12][13][14]. In the present high-pressure experiments, a very small amount of C 2 H 5 NO 2 − was detected occasionally.…”

“…The C 2 H 4 NO 2 − ion is not observed under collision-free conditions [12][13][14]. In the present study, this species is assumed to be produced by several exothermic proton transfer reactions, such as…”

“…Lunt et al [11] measured absolute total integral and total backward scattering cross-sections for C 2 H 5 NO 2 in the energy range from 50 meV to 1.2 eV. Dissociative electron attachment to C 2 H 5 NO 2 has been the subject of several investigations [12][13][14]. In a recent study, Märk and co-workers [14] reported the absolute partial cross-sections for the formation of eight fragment negative ions (NO 2 − , C 2 H 3 NO 2 − , O − , OH − , CN − , CNO − , HCN − and NO − ) by electron attachment to C 2 H 5 NO 2 in the gaseous phase under collision-free conditions.…”

Dissociative electron attachment to nitroethane: C2H5NO2

“…We are aware of only two previous DEA studies concerning nitroethane. 2, 3 Jäger and Henglein 2 performed in 1967 a first experimental study concerning DEA to nitroethane in an electron energy range from about 0 to 10 eV using a sector field mass spectrometer with a pulsed Fox electron impact ion source with an estimated energy spread of less than 200 meV. They observed six fragment negative ions (NO 2 Ϫ ,C 2 H 3 NO 2 Ϫ ,O Ϫ ,OH Ϫ ,CN Ϫ ,CNO Ϫ ) and gave rough estimates of the corresponding cross sections.…”

“…They observed six fragment negative ions (NO 2 Ϫ ,C 2 H 3 NO 2 Ϫ ,O Ϫ ,OH Ϫ ,CN Ϫ ,CNO Ϫ ) and gave rough estimates of the corresponding cross sections. Tsuda et al 3 employing a mass spectrometer without an electron monochromator to improve the energy spread from a rhenium filament measured the negative ion yields for the negative ions NO 2 Ϫ , CH 2 NO 2 Ϫ , O Ϫ , CN Ϫ and CNO Ϫ in the electron energy range from about 3 to 30 eV. They were not able to measure the negative ion yield below 3 eV.…”