Probing Nonadiabatic Dynamics with Attosecond Pulse Trains and Soft X-ray Raman Spectroscopy

TL;DR

This study explores the use of attosecond pulse trains generated by high-harmonic generation as probes in X-ray Raman spectroscopy to detect ultrafast electronic coherences during nonadiabatic molecular dynamics.

Contribution

It demonstrates the effectiveness of attosecond pulse trains in capturing electronic coherence features, expanding the capabilities of X-ray Raman spectroscopy with novel pulse schemes.

Findings

Pulse trains effectively detect electronic coherences.

Pulse parameters influence spectral signals.

Symmetry and vibrational effects are significant.

Abstract

Linear off-resonant X-ray Raman techniques are capable of detecting the ultrafast electronic coherences generated when a photoexcited wave packet passes through a conical intersection. A hybrid femtosecond or attosecond probe pulse is employed to excite the system and stimulate the emission of the signal photon, where both fields are components of a hybrid pulse scheme. In this paper, we investigate how attosecond pulse trains, as provided by high-harmonic generation processes, perform as probe pulses in the framework of this spectroscopic technique, instead of single Gaussian pulses. We explore different combination schemes for the probe pulse, as well as the impact of parameters of the pulse trains on the signals. Furthermore, we show how Raman selection rules and symmetry consideration affect the spectroscopic signal, and we discuss the importance of vibrational contributions to the overall signal. We use two different model systems, representing molecules of different symmetry, and quantum dynamics simulations to study the difference in the spectra. The results suggest that such pulse trains are well suited to capture the key features associated with the electronic coherence.