Excitation, two-center interference and the orbital geometry in laser-induced nonsequential double ionization of diatomic molecules

TL;DR

This paper investigates how molecular orbital geometry and alignment affect nonsequential double ionization in diatomic molecules, revealing interference patterns and orbital shape effects on electron momentum distributions.

Contribution

It provides analytical expressions for two-center interference maxima/minima considering orbital mixing and geometry, and analyzes how alignment influences these interference patterns.

Findings

Interference maxima and minima depend on molecular alignment and orbital geometry.

Sharp interference patterns occur at zero alignment angle and diminish with increased angle.

Orbital shape causes suppression in momentum regions and reduces RESI yield.

Abstract

We address the influence of the molecular orbital geometry and of the molecular alignment with respect to the laser-field polarization on laser-induced nonsequential double ionization of diatomic molecules for different molecular species, namely $\mathrm{N}_2$ and $\mathrm{Li}_2$. We focus on the recollision excitation with subsequent tunneling ionization (RESI) mechanism, in which the first electron, upon return, promotes the second electron to an excited state, from where it subsequently tunnels. We show that the electron-momentum distributions exhibit interference maxima and minima due to the electron emission at spatially separated centers. We provide generalized analytical expressions for such maxima or minima, which take into account $s$ $p$ mixing and the orbital geometry. The patterns caused by the two-center interference are sharpest for vanishing alignment angle and get washed out as this parameter increases. Apart from that, there exist features due to the geometry of the lowest occupied molecular orbital (LUMO), which may be observed for a wide range of alignment angles. Such features manifest themselves as the suppression of probability density in specific momentum regions due to the shape of the LUMO wavefunction, or as an overall decrease in the RESI yield due to the presence of nodal planes.