Dissociative Electron Attachment to Formamide: Direct and Indirect Pathways from Resonant Intermediates
Dissociative Electron Attachment to Formamide: Direct and Indirect Pathways from Resonant Intermediates
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DOI：
10.1021/ct800379h
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发表时间：
2009-01-01
影响因子：
5.5
通讯作者：
Rivail, J. L.
中科院分区：
文献类型：
--
作者：
Goumans, T. P. M.;Gianturco, F. A.;Rivail, J. L.
通过电子-分子散射计算研究甲酰胺 (HCONH2)（具有肽键的最小分子）的解离电子附着 (DEA)。在平衡几何结构中，我们分别在 3.77 eV 和 14.90 eV 处确定了 A'' 和 A' 对称的两个共振。为了进一步评估瞬态负离子 (TNIs) 的潜在断键途径，研究了 C-H 和 C-N 键键拉伸时的共振行为。虽然沿着 C-H 解离坐标，共振都没有显着变化，但我们发现，在拉伸肽 C-N 键时，两种共振都稳定下来，它们的共振能量和宽度迅速下降，对于 A' 共振来说最为强烈。因此，当 C-N 键拉伸超过 1 A 时，可以看到 A' 共振消失，此时它可能平滑地连接到结合阴离子状态，这是 A' TNI 产生 NH2- 和 HCO 的直接 DEA 途径。发现 A'' 共振并不是沿着 C-N 坐标纯粹解离，而是演变成在 NH2 片段上形成低位共振。此外，对称性考虑表明传入电子将自身附着到 NH2 和 HCO 渐近碎片的 A' 对称轨道上。因此，来自 A" TNI 的 DEA 必须通过对称性破缺的非绝热曲线交叉发生，该曲线交叉连接到纯解离的 A' 亚稳态阴离子态，该阴离子态随着键拉伸的发生而能量下降。
Dissociative electron attachment (DEA) to formamide (HCONH2), the smallest molecule with a peptide bond, is investigated with electron-molecule scattering calculations. At the equilibrium geometry we identify two resonances of A '' and A' symmetry at 3.77 and 14.90 eV, respectively. To further assess potential bond-breaking pathways for the transient negative ions (TNIs), the behavior of the resonances upon bond stretching of the C-H and C-N bond is investigated. While along the C-H dissociation coordinate neither resonance changes significantly, we find instead that both resonances are stabilized upon stretching the peptide C-N bond, with their resonance energy and width coming down rapidly, most strongly so for the A' resonance. The A' resonance is thus seen to disappear when the C-N bond is stretched for more than 1 A, where it presumably smoothly connects to a bound anion state, a direct DEA pathway for the A' TNI to yield NH2- and HCO. The A '' resonance is found instead not to be purely dissociative along the C-N coordinate but to evolve into forming a low-lying resonance on the NH2 fragment. Furthermore, symmetry considerations dictate here that the incoming electron attaches itself to an orbital of A' symmetry of the NH2 and HCO asymptotic fragments. Therefore, DEA from the A" TNI has to occur via a symmetry-breaking, nonadiabatic curve crossing which connects to the purely dissociative A' metastable anionic state that is coming down in energy as the bond stretching occurs.