Imaging Purely Nuclear Quantum Dynamics in Molecules by Combined X-ray and Electron Diffraction

Abstract

Monitoring the motions of atoms and molecules in the course of chemical processes is a central goal of femtochemistry. Optical spectroscopic signals are usually sensitive to electronic properties such as dipoles, polarizabilities, and electronic charge densities rather than to nuclear motions. In this theoretical study, we propose a novel measurement that solely and directly monitors the evolving nuclear wave packet and can thereby unambiguously image photochemical events in real time. We demonstrate how nuclear charge densities can be singled out by subtracting the ultrafast gas-phase X-ray and electron diffraction signals in the photodissociation of thiophenol as it passes through two conical intersections. This signal can reveal the shape and trajectory of the nuclear wave packets as well as the electronic coherences in the vicinity of conical intersections.

Attosecond Charge Migration in Molecules Imaged by Combined X-ray and Electron Diffraction

“…The electron dynamics in Figure 2 is well captured by the MENIED simulated in Figure 3 (full simulated signals are given in the SI as video files). Diffraction patterns in Figure 3 show clear interfering beating features that are characteristic in heterodyne diffraction signals, 30,38 demonstrating the selfheterodyne nature of the ΔS diff (q, t) signal in eq 10. This can be interpreted as heterodyne detection of the electronic charge density where the nuclear structure serves as a local reference.…”

“…Previously, we have shown how to image the purely nuclear charge density by combining heterodyne-detected X-ray and electron diffraction. 38 The proposed experimental scheme in Figure 1 is much easier to implement, as heterodyne detections are not required in this study. We show that, when subtracting the ultrafast X-ray and electron homodyne diffraction signals, the time-dependence of the signal only comes from a mixed nuclear−electronic term σ E σ N where σ E/N is the electronic/ ■ THEORY OF MIXED ELECTRONIC−NUCLEAR…”

Time-resolved X-ray and XUV based spectroscopic methods for nonadiabatic processes in photochemistry

“…In recent theoretical studies, X-ray and electron diffraction were used to study nuclear dynamics in the vicinity of CIs. 55,56,107 The use of a resonant infrared (IR) pulse combined with an X-ray diffraction pulse has been recently proposed to enhance the features of coherences in the vicinity of a CI. 108 Recently, a time-resolved orbital angular momentum X-ray pulse diffraction technique was proposed.…”

“…53 Time-resolved X-ray diffraction (XRD) has been implemented theoretically to spatially detect the occurrence of nonadiabatic dynamics in a molecule. 54–56 Besides X-ray based methods, time-resolved photoelectron spectroscopy (TRPES) has been shown capable of observing the population transfer and studying the electronic coherence created in the vicinity of a CI. 57–60…”

“…53 Time-resolved X-ray diffraction (XRD) has been implemented theoretically to spatially detect the occurrence of nonadiabatic dynamics in a molecule. [54][55][56] Besides X-ray based methods, time-resolved photoelectron spectroscopy (TRPES) has been shown capable of observing the population transfer and studying the electronic coherence created in the vicinity of a CI. [57][58][59][60] In this feature article, we want to give an overview of these novel time-resolved spectroscopic techniques that can be used to study dynamics in the vicinity of CI.…”