Multi-photon above threshold ionization of multi-electron atoms and molecules using the R-matrix approach

Jakub Benda,Zdeněk Mašín

doi:10.1038/s41598-021-89733-z

Abstract

We formulate a computationally efficient time-independent method based on the multi-electron molecular R-matrix formalism. This method is used to calculate transition matrix elements for the multi-photon ionization of atoms and molecules under the influence of a perturbative field. The method relies on the partitioning of space which allows us to calculate the infinite-range free-free dipole integrals analytically in the outer region, beyond the range of the initial bound wave function. This approach is valid for an arbitrary order, that is, any number of photons absorbed both in the bound and the continuum part of the spectrum (below- and above-threshold ionization). We calculate generalized multi-photon cross sections and angular distributions of different systems (H, He, hbox {H}_{{2}}, hbox {CO}_{{2}}) and validate our approach by comparison with data from the literature.

Highlights

We formulate a computationally efficient time-independent method based on the multi-electron molecular R-matrix formalism
Multi-photon ionization (MPI) and its variant resonance-enhanced multi-photon ionization (REMPI) in atoms and molecules have a range of important applications ranging from laser-induced plasma g eneration[1,2], chemical diagnostics[3,4,5], chiral r ecognition[6,7,8,9,10] to laser-filamentation11–15, harmonic[16,17,18] and high-harmonic[19] generation and photoelectron spectroscopy[20]
After a brief review of the computational method in the two sections, we present results for multi-photon ionization of helium, molecular hydrogen and carbon dioxide across a continuous range of photon energies probing REMPI and non-resonant MPI

Summary

Introduction

We formulate a computationally efficient time-independent method based on the multi-electron molecular R-matrix formalism. The method is based on the R-matrix approach, which accurately solves the time-independent Schrödinger equation in the close vicinity of the target system (atom, molecule, molecular cluster, ...) and uses an analytic asymptotic expansion of the wave function elsewhere.

Results

Conclusion