Multiphoton Photoelectron Circular Dichroism of Limonene with Independent Polarization State Control of the Bound-Bound and Bound-Continuum Transitions

TL;DR

This study investigates how independent control of polarization states in multiphoton ionization affects photoelectron circular dichroism in chiral limonene molecules, revealing the dominant role of bound-bound transition anisotropy.

Contribution

It demonstrates that bound-bound transition anisotropy significantly influences PECD, while the helicity of the bound-bound transition has minimal effect, advancing understanding of chiroptical effects in multiphoton ionization.

Findings

Bound-bound transition anisotropy affects PECD magnitude.

Helicity of bound-bound transition has negligible impact on PECD.

Photoexcitation anisotropy depends on laser polarization states.

Abstract

Photoionization of randomly oriented chiral molecules with circularly polarized light leads to a strong forward/backward asymmetry in the photoelectron angular distribution. This chiroptical effect, referred to as Photoelectron Circular Dichroism (PECD), was shown to take place in all ionization regimes, from single photon to tunnel ionization. In the Resonance Enhanced Multiphoton Ionisation (REMPI) regime, where most of the table-top PECD experiments have been performed, understanding the role of the intermediate resonances is currently the subject of experimental and theoretical investigations. In an attempt to decouple the role of bound-bound and bound-continuum transitions in REMPI-PECD, we photoionized the (+)-limonene enantiomer using two-color laser fields in [1+1'] and [2+2'] ionization schemes, where the polarization state of each color can be controlled independently. We demonstrate that the main effect of the bound-bound transition is to break the sample isotropy by orientation-dependent photoexcitation, in agreement with recent theoretical pre- dictions. We show that the angular distribution of PECD strongly depends on the anisotropy of photoexcitation to the intermediate state, which is different for circularly and linearly polarized laser pulses. On the contrary, the helicity of the pulse that drives the bound-bound transition is shown to have a negligible effect on the PECD.