Ultrafast strong-field dissociation of vinyl bromide: An attosecond transient absorption spectroscopy and non-adiabatic molecular dynamics study

Abstract

Attosecond extreme ultraviolet (XUV) and soft x-ray sources provide powerful new tools for studying ultrafast molecular dynamics with atomic, state, and charge specificity. In this report, we employ attosecond transient absorption spectroscopy (ATAS) to follow strong-field-initiated dynamics in vinyl bromide. Probing the Br M edge allows one to assess the competing processes in neutral and ionized molecular species. Using ab initio non-adiabatic molecular dynamics, we simulate the neutral and cationic dynamics resulting from the interaction of the molecule with the strong field. Based on the dynamics results, the corresponding time-dependent XUV transient absorption spectra are calculated by applying high-level multi-reference methods. The state-resolved analysis obtained through the simulated dynamics and related spectral contributions enables a detailed and quantitative comparison with the experimental data. The main outcome of the interaction with the strong field is unambiguously the population of the first three cationic states, D 1 , D 2 , and D 3 . The first two show exclusively vibrational dynamics while the D 3 state is characterized by an ultrafast dissociation of the molecule via C–Br bond rupture within 100 fs in 50% of the analyzed trajectories. The combination of the three simulated ionic transient absorption spectra is in excellent agreement with the experimental results. This work establishes ATAS in combination with high-level multi-reference simulations as a spectroscopic technique capable of resolving coupled non-adiabatic electronic-nuclear dynamics in photoexcited molecules with sub-femtosecond resolution.

Core-Excited States and X-ray Absorption Spectra from Multireference Algebraic Diagrammatic Construction Theory

“…While this assumption is valid for many closed-shell molecules at (or near) equilibrium geometries, XAS is increasingly being used to probe core-level excited states of chemical systems with more challenging electronic structures, such as radicals, − transition-metal complexes, − and along the dissociative reaction pathways − where multireference effects can be significant. However, in contrast to single-reference theories, the range of available multireference methods is much narrower, including implementations of multiconfigurational self-consistent field, − multireference perturbation theories, − configuration interaction, − coupled cluster, ,− and driven similarity renormalization group approaches. − …”

Conical intersection and coherent vibrational dynamics in alkyl iodides captured by attosecond transient absorption spectroscopy

“…The Journal of Chemical Physics ARTICLE scitation.org/journal/jcp crossings [9][10][11][12][13][14] as well as of molecular vibrations with sub-angstrom precision. [15][16][17] In this study, the sensitivity of ATAS to electronic and nuclear dynamics enables the observation of conical intersection dynamics in the A-band photodissociation of alkyl iodides (R-I, R = CnHm).…”

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

“…If a resonant excitation is not possible in the experiment and non-resonant strong field pump-pulses are used, TXAS still provides detailed insights into the electronic-state-resolved dynamics. 70 The valence-to-core excitation frequency changes as the nuclei evolve in an excited state PES. By varying the pump–probe delay, the information of the absorbed photons is used to follow the nuclear dynamics.…”