High-resolution measurements of the positronium formation cross sections for positron energies from threshold to 10 eV are presented for aniline (${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{NH}}_2$), pyridine (${\mathrm{C}}_5{\mathrm{H}}_5\mathrm{N}$), and cyclopentane (${\mathrm{C}}_5{\mathrm{H}}_{10}$). The data reveal that the measured energy dependence of the cross sections on the excess energy in the near-threshold region (1–2 eV) is nearly identical to that of the corresponding photoionization cross sections. This similarity occurs despite the difference between the basic threshold laws for processes without and with a Coulomb interaction between the final-state particles. It is proposed here that the near-threshold behavior of these two different ionization processes is governed by the vibrational dynamics of the final-state cation. This is supported by comparison of the data with the calculated spectrum of vibronic intensities for the pyridine cation [Trofimov et al., J. Chem. Phys. 153, 164307 (2020)].

中文翻译：

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分子中正电子形成和光电离的近阈值能量依赖性的相似性


苯胺的正电子能量从阈值到 10 eV 的正电子形成横截面的高分辨率测量（ ${\mathrm{C}}_6{\mathrm{H}}_5{\mathrm{NH}}_2$ ), 吡啶 ( ${\mathrm{C}}_5{\mathrm{H}}_5\mathrm{N}$ ）和环戊烷（ ${\mathrm{C}}_5{\mathrm{H}}_{10}$ ）。数据表明，测量到的截面能量对近阈值区域（1-2 eV）多余能量的依赖性与相应的光电离截面的能量依赖性几乎相同。尽管最终态粒子之间没有库仑相互作用和有库仑相互作用的过程的基本阈值定律之间存在差异，但这种相似性仍然存在。这里提出，这两种不同电离过程的近阈值行为由最终态阳离子的振动动力学控制。通过将数据与计算的吡啶阳离子电子振动强度谱进行比较来支持这一点[Trofimov等人，2017]。 ， J.化学。物理。 153、164307 （2020）]。