Alignment dependent enhancement of the photo-electron cutoff for multi-photon ionization of molecules

TL;DR

This paper investigates how molecular alignment influences the high-energy cutoff in photo-electron spectra during multi-photon ionization, revealing that alignment can enhance electron energies under certain conditions.

Contribution

It demonstrates the alignment-dependent enhancement of photo-electron cutoff energies in molecules, supported by experimental data and tunneling model calculations.

Findings

Alignment can increase the photo-electron cutoff energy.

Nodal plane probing enhances high-energy electrons.

Tunneling model supports experimental observations.

Abstract

The multiphoton ionization rate of molecules depends on the alignment of the molecular axis with respect to the ionizing laser polarization. By studying molecular frame photo-electron angular distributions from N$_2$, O$_2$ and benzene, we illustrate how the angle-dependent ionization rate affects the photo-electron cutoff energy. We find alignment can enhance the high energy cutoff of the photo-electron spectrum when probing along a nodal plane or when ionization is otherwise suppressed. This is supported by calculations using a tunneling model with a single ion state.