Attosecond timing of electron emission from a molecular shape resonance

TL;DR

This study uses attosecond interferometry to measure how nuclear motion in N₂ affects electron emission timing from a shape resonance, revealing that tiny nuclear changes can cause significant delays in ionization.

Contribution

It demonstrates a novel attosecond measurement technique to observe nuclear influence on electron emission timing in molecular shape resonances.

Findings

Nuclear motion causes up to 200 attoseconds delay in ionization.

Tiny bond length changes significantly affect electron emission timing.

The results challenge the assumption of instantaneous electronic transitions in molecules.

Abstract

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$_2$. 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.