近日，德国马克斯·普朗克核物理研究所的Viviane C. Schmidt及其研究团队取得一项新进展。经过不懈努力，他们揭示高旋转激发下双原子碳阴离子的单分子过程。相关研究成果已于2024年10月31日在国际知名学术期刊《物理评论A》上发表。

在毫秒到秒的时间尺度上，从溅射离子源中储存的双原子碳负离子C₂^-表现出通过电子发射和碎裂产生的单分子衰变，其原因尚不明朗。为了解释实验速率的量级和时间依赖性，研究人员为C₂^-的最低电子态（包括最低的四重态电位）建立了具有高转动和振动激发的能级模型。

研究人员确定了大量高度激发的C₂^-能级的能量、自发辐射衰变速率（包括自旋禁阻的四重态能级衰变）以及隧穿解离速率，并考虑了这些能级在溅射型离子源中的布居情况。对于四重态能级，研究人员探讨了其抗自脱附稳定性，并应用了最近计算的转动辅助自脱附速率。

此外，研究人员还计算了双重态C₂^-基态电位中高振动能级的非绝热振动自脱附速率。研究人员将这些结果结合起来，以模拟实验观察到的单分子衰变信号。将模型预测结果与在低温储存环设施CSR测得的实验速率进行比较后，有力证据表明，四重态电子态中准稳定能级上的C₂^-离子是迄今为止尚未确定的单分子衰变来源。

附：英文原文

Title: Unimolecular processes in diatomic carbon anions at high rotational excitation

Author: Viviane C. Schmidt, Roman urík, Milan Onák, Klaus Blaum, Sebastian George, Jürgen Gck, Manfred Grieser, Florian Grussie, Robert von Hahn, Claude Krantz, Holger Kreckel, Oldich Novotny, Kaija Spruck, Andreas Wolf

Issue&Volume: 2024/10/31

Abstract: On the millisecond to second time scale, stored beams of diatomic carbon anions C₂^- from a sputter ion source feature unimolecular decay of yet unexplained origin by electron emission and fragmentation. To account for the magnitude and time dependence of the experimental rates, levels with high rotational and vibrational excitation are modeled for the lowest electronic states of C₂^-, also including the lowest quartet potential. Energies, spontaneous radiative decay rates (including spin-forbidden quartet-level decay), and tunneling dissociation rates are determined for a large number of highly excited C₂^- levels and their population in sputter-type ion sources is considered. For the quartet levels, the stability against autodetachment is addressed and recently calculated rates of rotationally assisted autodetachment are applied. Nonadiabatic vibrational autodetachment rates of high vibrational levels in the doublet C₂^- ground potential are also calculated. The results are combined to model the experimental unimolecular decay signals. Comparison of the modeled to the experimental rates measured at the cryogenic storage ring facility CSR gives strong evidence that C₂^- ions in quasistable levels of the quartet electronic states are the so far unidentified source of unimolecular decay.

DOI: 10.1103/PhysRevA.110.042828

Source: https://journals.aps.org/pra/abstract/10.1103/PhysRevA.110.042828