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

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.

Theoretical Investigation of Dissociative Electron Attachment of Acrylonitrile

“…17 The present peak at 6.8 eV is consistent with the peak reported at 6.6 eV by Heni and Illenberger. 17 While considering the ion current curves of Tsuda et al 16 and Sugiura et al, 15 we realized that both the curves begin appearing at 5.0 eV (same as in the present case) but do not observe maximum at 6.8 eV. According to Tsuda et al, 16 the first process can be ascribed to the reaction…”

“…In this case, AP cal is calculated using ΔH f (C 2 H 2 ) = 2.35 eV and ΔH f (H) = 2.26 eV. 37 Thus, the present AP of 3.6 eV is close to 3.50 eV reported by Sugiura et al 15 and 3.8 eV seen in Heni and Illenberger's 17 ion yield curve but slightly higher than the value of 3 eV reported by Tsuda et al 16 The present second peak at 4.5 eV is exactly the same as the 4.5 eV peak of Heni and Illenberger 17 and lower compared to 4.9 eV and 5.1 eV extracted from the ion yield curves of Sugiura et al 15 and Tsuda et al, 16 respectively. The third resonant process starts appearing at 5.9 eV in the present case, and its peak value is at 8.4 eV.…”

“…The existing dissociation peak at 1.5 eV can be thus correlated with one-particle shape resonance observed at 1.4 eV in our previous cross-sectional study on acrylonitrile. 21 The second resonant process in Figure 3 starts appearing at 3.6 eV, and its peak is observed at 4.5 eV; the possible reaction for this resonant process 16 is given below…”

Negative ion chemistry in Titan's upper atmosphere

“…Comparison of the yield of CN -ions with that of C 2 H 3 CN + gave the value 47.6 for C 2 H 3 CN + /CN -at 9.5 eV (15 eV for the positive ions) (Tsuda et al, 1973). The total impact cross section of C 2 H 3 CN is unknown and we have estimated it to be equal to that of C 4 H 2 (Kim and Irikura, 2000).…”

“…The cross section for formation of CN -is small with peak values of ~4 10 -21 cm 2 at 1.8 eV and ~10 -20 cm 2 at 9.2 eV. For acrylonitrile (C 2 H 3 CN), the CN -yield curve exhibits 3 peaks at ~2, ~3 and ~6 eV (Heni and Illenberger, 1986;Tsuda et al, 1973).…”