Electron correlation driven non-adiabatic relaxation in molecules excited by an ultrashort extreme ultraviolet pulse

Abstract

The many-body quantum nature of molecules determines their static and dynamic properties, but remains the main obstacle in their accurate description. Ultrashort extreme ultraviolet pulses offer a means to reveal molecular dynamics at ultrashort timescales. Here, we report the use of time-resolved electron-momentum imaging combined with extreme ultraviolet attosecond pulses to study highly excited organic molecules. We measure relaxation timescales that increase with the state energy. High-level quantum calculations show these dynamics are intrinsic to the time-dependent many-body molecular wavefunction, in which multi-electronic and non-Born−Oppenheimer effects are fully entangled. Hints of coherent vibronic dynamics, which persist despite the molecular complexity and high-energy excitation, are also observed. These results offer opportunities to understand the molecular dynamics of highly excited species involved in radiation damage and astrochemistry, and the role of quantum mechanical effects in these contexts.

Theoretical investigation of the electronic relaxation in highly excited chrysene and tetracene: The effect of armchair vs zigzag edge

“…where A = min[P IS (t)]/(1 + min[P IS (t)]) and B = 1/(1 + min[P IS (t)]). This new fitting procedure, adapted from the work of Marciniak et al 37 , allows one to fit the initial population more accurately thanks to the shift A, which takes into account the non-vanishing population at the end of the simulation (e.g. non-Kasha behaviour).…”

“…Beyond the determination of vertical spectra, experimental setups have been designed, to explore the postexcitation dynamics of systems as large as PAHs with femtosecond resolution. [35][36][37] From the theoretical side, a number of studies have been focused on the static calculations of excited states in cationic PAHs and their possible non-radiative relaxation towards the ground state. [38][39][40] More recently, multi-state non-adiabatic molecular dynamics (NAMD) of small cationic polyacenes have been investigated, coupling the electronic and nuclei motion.…”

Approaching black-box calculations of pump-probe fragmentation dynamics of polyatomic molecules

“…An understanding of these types of experiments can be obtained through the framework of explicitly simulating the underlying processes. [14,15,16] In this paper, we focus on a theoretical description of pump-probe experiments used to investigate the fragmentation dynamics of molecules. The most straightforward way is to simulate femtosecond chemical responses based on the quantum mechanical treatment of the nuclear motions in several electronic states (beyond the Born-Oppenheimer approximation).…”

Non-adiabatic molecular dynamics investigation of the size dependence of the electronic relaxation in polyacenes

“…[24,25,23] This motivated several experimental and theoretical investigations of their photoabsorption and dynamical properties. [24,25,26,27,28,29,30,31,32,33] However, less information about photophysics of neutral PAH molecules is available, despite the fact that they cannot be excluded from contributing to the DIBs. In addition, their photostability has to be studied as well as the efficiency of non-radiative relaxation pathways, which is usually assumed to be fast enough to quickly drive the system into a vibrationally hot electronic ground state (GS).…”

“…This work is also motivated by the recent development of experimental tools allowing to probe femtosecond dynamics of this type of molecules. [39,40,41,32,33] The paper is organized as follows: in the next section, we briefly outline the basics of DFTB and TD-DFTB as well as some computational and implementation details. Subsequently, the results and discussions are devoted to the application to polyacenes, first assessing the quality of the TD-DFTB for calculating their absorption spectra prior to analyzing the non-adiabatic dynamics for each molecular system.…”