Nandi S, Plésiat E, Zhong S, Palacios A, Busto D, Isinger M, Neoričić L, Arnold C L, Squibb R J, Feifel R, Decleva P, L'Huillier A, Martín F, Gisselbrecht M
Department of Physics, Lund University, 22100 Lund, Sweden.
Université de Lyon, Université Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, F-69622 Villeurbanne, France.
Sci Adv. 2020 Jul 31;6(31):eaba7762. doi: 10.1126/sciadv.aba7762. eCollection 2020 Jul.
Shape resonances in physics and chemistry arise from the spatial confinement of a particle by a potential barrier. In molecular photoionization, these barriers prevent the electron from escaping instantaneously, so that nuclei may move and modify the potential, thereby affecting the ionization process. By using an attosecond two-color interferometric approach in combination with high spectral resolution, we have captured the changes induced by the nuclear motion on the centrifugal barrier that sustains the well-known shape resonance in valence-ionized N. We show that despite the nuclear motion altering the bond length by only 2%, which leads to tiny changes in the potential barrier, the corresponding change in the ionization time can be as large as 200 attoseconds. This result poses limits to the concept of instantaneous electronic transitions in molecules, which is at the basis of the Franck-Condon principle of molecular spectroscopy.
物理学和化学中的形状共振源于粒子被势垒的空间限制。在分子光电离中，这些势垒阻止电子瞬间逃逸，使得原子核可以移动并改变势，从而影响电离过程。通过将阿秒双色干涉测量方法与高光谱分辨率相结合，我们捕捉到了核运动在维持价态电离氮中著名形状共振的离心势垒上引起的变化。我们表明，尽管核运动仅使键长改变2%，这导致势垒的微小变化，但电离时间的相应变化可能高达200阿秒。这一结果对分子中瞬时电子跃迁的概念提出了限制，而该概念是分子光谱学中弗兰克 - 康登原理的基础。
