Attosecond photoionisation time delays reveal the anisotropy of the molecular potential in the recoil frame

H Ahmadi,P Decleva,L Poletto,F Martin,M Moioli,C D Schröter,E Plésiat,F Frassetto,A Palacios,T Pfeifer,R Moshammer,G Sansone

doi:10.1038/s41467-022-28783-x

Abstract

Photoionisation time delays carry structural and dynamical information on the target system, including electronic correlation effects in atoms and molecules and electron transport properties at interfaces. In molecules, the electrostatic potential experienced by an outgoing electron depends on the emission direction, which should thus lead to anisotropic time delays. To isolate this effect, information on the orientation of the molecule at the photoionisation instant is required. Here we show how attosecond time delays reflect the anisotropic molecular potential landscape in CF4 molecules. The variations in the measured delays can be directly related to the different heights of the potential barriers that the outgoing electrons see in the vicinity of shape resonances. Our results indicate the possibility to investigate the spatial characteristics of the molecular potential by mapping attosecond photoionisation time delays in the recoil-frame.

Highlights

Photoionisation time delays carry structural and dynamical information on the target system, including electronic correlation effects in atoms and molecules and electron transport properties at interfaces
The dynamics of photoionising wave packets is usually investigated by means of pump-probe experiments, in which an isolated or a train of attosecond pulses in the extreme ultraviolet (XUV) range set the photoelectron wave packet free and a synchronised infra-red (IR) pulse probes the instant at which the electron enters the continuum[8]
Attosecond time delays have been reported in photoionisation in molecular systems, showing the relevance of nuclear motion in hydrogen[12] and the role played by shape resonances in N2O13 and nitrogen[14,15]

Summary

Introduction

Photoionisation time delays carry structural and dynamical information on the target system, including electronic correlation effects in atoms and molecules and electron transport properties at interfaces. In this work we investigate the photoionisation dynamics induced by a train of attosecond XUV pulses on CF4 molecules by means of photoelectron-photoion coincidence spectroscopy[23] The advantage of this approach is the possibility to derive information on the molecular orientation at the instant of photoionisation by measuring in coincidence the momenta of the emitted electron and the fragment ions resulting from the ulterior dissociation of the molecular cation[24]. In this way, we have been able to unambiguously identify individual ionisation channels and obtain time-resolved recoil-frame photoelectron angular distributions (RFPADs) from which the variations of photoionisation delays with the electron emission direction have been extracted. The agreement confirms the validity of our experimental approach and opens the route to orientation-specific exploration and understanding of molecular photoionisation delays

Methods

Results

Conclusion