Series of molecular-like doubly excited states of a quasi-three-body Coulomb system

TL;DR

This paper explores highly doubly excited states in a quasi-three-body Coulomb system, revealing molecular-like electron correlations and providing both experimental and theoretical insights into their structure and dynamics.

Contribution

It introduces a new series of molecular-like doubly excited states in a Coulomb system, supported by experimental data and first-principles calculations, with a simple model explaining their correlated motion.

Findings

Identification of a series of doubly excited states converging to the double ionization threshold

Reproduction of these states through first-principles calculations

Proposal of a molecular-like adiabatic model for electron correlation

Abstract

We investigated resonant multiphoton excitation of high-angular-momentum planetary states of the strontium atom, a quasi-three-body Coulomb system, both experimentally and theoretically. A series of highly doubly excited electronic states converging to the double ionization threshold was identified and reproduced by first-principles calculations, which provided access to the two-electron wavefunctions of the resonances. In these states, the outer electron is dynamically localized at large distances by pendulum-like oscillations of the inner electron across the nucleus. A complementary simple molecular-like adiabatic model offers a clear interpretation of the correlated two-electron motion and suggests that the series is a general feature of highly doubly excited states of atoms and molecules.