Molecular structure retrieval directly from laboratory-frame photoelectron spectra in laser-induced electron diffraction

A Sanchez,B Belsa,J Ullrich,R Moshammer,X Liu,T Pfeifer,A T Le,C D Lin,J Danek,S Gräfe,S.-J Wang,J Biegert,T Steinle,K Amini,M Richter

doi:10.1038/s41467-021-21855-4

Abstract

Ubiquitous to most molecular scattering methods is the challenge to retrieve bond distance and angle from the scattering signals since this requires convergence of pattern matching algorithms or fitting methods. This problem is typically exacerbated when imaging larger molecules or for dynamic systems with little a priori knowledge. Here, we employ laser-induced electron diffraction (LIED) which is a powerful means to determine the precise atomic configuration of an isolated gas-phase molecule with picometre spatial and attosecond temporal precision. We introduce a simple molecular retrieval method, which is based only on the identification of critical points in the oscillating molecular interference scattering signal that is extracted directly from the laboratory-frame photoelectron spectrum. The method is compared with a Fourier-based retrieval method, and we show that both methods correctly retrieve the asymmetrically stretched and bent field-dressed configuration of the asymmetric top molecule carbonyl sulfide (OCS), which is confirmed by our quantum-classical calculations.

Highlights

Ubiquitous to most molecular scattering methods is the challenge to retrieve bond distance and angle from the scattering signals since this requires convergence of pattern matching algorithms or fitting methods
While the zero crossing points (ZCPs)-laserinduced electron diffraction (LIED) method has been demonstrated for the structural retrieval of the OCS molecule only, we believe that the present work offers two important implications which deserve further discussion
Since molecular bond lengths enter explicitly only in the phase of the interfering terms, by analysing only the ZCPs, the ZCP-LIED method relaxes the limitation of the Born approximation or the independent atom model (IAM) that are at the heart of electron diffraction theory

Summary

Introduction

Ubiquitous to most molecular scattering methods is the challenge to retrieve bond distance and angle from the scattering signals since this requires convergence of pattern matching algorithms or fitting methods. Variation of the pulse duration gives access to probing different dynamics, e.g. to distinguish between linear or bent stretching dynamics in OCS, or to probe the dynamics of the neutral molecule[22] Notwithstanding these advances, extraction of the molecular structure from a measured electron interference pattern still requires some sort of pattern matching or minimization procedure, which can lead to molecular parameters with significant variances depending on the exact topography of extremal points in the solution space obtained from measured diffraction images. We note that this is a general challenge for all scattering-based methods, and not unique to LIED.

Methods

Results

Conclusion