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

TL;DR

This paper introduces an efficient R-matrix based method for calculating multi-photon ionization processes in atoms and molecules, capable of handling any photon order and validated against existing data.

Contribution

It develops a novel, space-partitioning R-matrix approach for multi-photon ionization, enabling accurate calculations of transition matrix elements for complex systems.

Findings

Validated method with H, He, H2, CO2

Accurate multi-photon cross sections and angular distributions

Applicable to any photon absorption order

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, H2, CO2) and validate our approach by comparison with data from the literature.