Break-down of the single-active-electron approximation for one-photon ionization of the B $^1\Sigma_u^+$ state of H$_2$ exposed to intense laser fields

TL;DR

This study investigates the ionization dynamics of the B $^1\, ext{Sigma}_u^+$ state of H$_2$ under intense laser fields, revealing a significant failure of the single-active-electron approximation due to poor continuum state modeling.

Contribution

It provides the first detailed comparison between full-dimensional simulations and simplified models for this molecular ionization process, highlighting the limitations of common approximations.

Findings

Single-active-electron approximation breaks down under intense fields.

Inadequate continuum state description causes the approximation failure.

Full-dimensional calculations reveal complex ionization dynamics.

Abstract

Ionization, excitation, and de-excitation to the ground state is studied theoretically for the first excited singlet state B $^1\Sigma_u^+$ of H$_2$ exposed to intense laser fields with photon energies in between about 3 eV and 13 eV. A parallel orientation of a linear polarized laser and the molecular axis is considered. Within the dipole and the fixed-nuclei approximations the time-dependent Schr\"odinger equation describing the electronic motion is solved in full dimensionality and compared to simpler models. A dramatic break-down of the single-active-electron approximation is found and explained to be due to the inadequate description of the final continuum states.