Measurement of Negative Ions Formed by Electron Impact. IX. Negative Ion Mass Spectra and Ionization Efficiency Curves of Negative Ions of m⁄e 25, 26, 27, 38, 39, 40 and 50 from Acrylonitrile

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Abstract
Negative ion mass spectra of acrylonitrile were measured for the electron energies of 80, 40 and 9.5 eV. Emphasis was laid on the abundance of the negative ions relative to the positive ions measured for the energies of 80, 40 and 15 eV, respectively. The ionization efficiency (IE) curves were also determined up to 25 eV for the ions of m⁄e 25(C2H−), 26(CN−), 27(HCN−), 38(C2N−), 39(CHCN−), 40(CH2CN−) and 50(C3N−). The electron impact of 80 eV and 40 eV gave almost the same distribution of m⁄e for negative ion mass spectra. Besides the most intense peak of CN− ions, relatively strong peaks of C3N−, C2H−, C2− and C2N− ions were observed. In 9.5 eV, CN− ions predominated over other ions. Yields of the ions showed a good linearity against the pressure in the range used for usual chemical analysis, irrespective of electron energy. Comparison of the yield of CN− ions with that of C2H3CN+ gave the values 1.2×104 and 1.9×104 for C2H3CN+/CN− at 80 eV and 40 eV, respectively, and 47.6 at 9.5 eV (15 eV for the positive ions). The plausible reaction schemes expected to occur at each onset observed in the IE curves were also sought thermochemically by using ΔHf values of the reactant and products. A value \gtrsim2 eV was obtained for the electron affinity of C2H.

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