Time-resolved x-ray scattering from impulsively aligned or oriented molecules

Abstract

Impulsive laser excitation of molecules can create rotational wave packets that lead to transient alignment or orientation. We present a theoretical analysis of the signatures of post-pulse field-free time-dependent alignment and orientation of diatomic molecules in time-resolved nonresonant x-ray scattering. This shows that alignment and its time dependence due to the interference terms of the rotational wave packet are visible in the x-ray scattering signal whereas signatures of orientation and its time dependence are absent. To that end, we discuss the time dependence of the coherent rotational motion associated with electronically resonant one-photon excitations. We illustrate our findings with calculated two-dimensional scattering signals for the sodium fluoride molecule (NaF) in the gas phase.

Mapping the photochemistry of cyclopentadiene: from theory to ultrafast X-ray scattering

“…31,32 The close relationship between the scattering signal and the twoelectron density implies that X-ray scattering could potentially constitute a sensitive probe of electron correlation. [57][58][59][60] Furthermore, cross terms between different electronic states i s j give rise to so-called coherent mixed scattering, which can provide interesting information on electron dynamics and coherences 31,61,62 and even electronic transitions at conical intersections. 63 However, this component is weak and has not been observed experimentally yet.…”

Ultrafast x-ray scattering and electronic coherence at avoided crossings: complete isotropic signals

“…We note that the pump pulse will make the sample slightly anisotropic due to preferential excitation along its polarisation vector. This leads to higher-order contributions to the scattering signal, most notably with l = 2 [10,39]. These anisotropic contributions, however, are usually much weaker than the isotropic component unless additional laser-driven alignment [7,11,98] is applied.…”

Probing the Effect of Molecular Structure Saddling on Ultrafast Charge Migration via Time-Resolved X-ray Diffraction

“…The availability of ultrashort, intense x-ray pulses from various free-electron laser sources around the globe [21,22] has opened a new array of possibilities to extend x-ray diffraction from static to time domain. TRXD is an emerging method to probe ultrafast processes in nature with atomic-scale spatial and temporal resolutions and has triggered significant theoretical [23][24][25][26][27][28][29][30][31][32][33][34] and experimental [35][36][37][38][39] research on TRXD from different molecules in recent years. Additionally, we will analyse time-dependent electronic flux densities to understand the mechanistic details of the charge migration associated with the induced dynamics.…”