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, D1, D2, and D3. The first two show exclusively vibrational dynamics while the D3 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.
Highlights
Since the demonstration of attosecond pulses, in the extreme ultraviolet (XUV) region of the electromagnetic spectrum (10–124 eV), via high-order harmonic generation (HHG), these pulses have been exploited for time-resolved investigations of ultrafast photoinitiated processes in atoms, molecules, and solids
Scitation.org/journal/sdy been exploited to take snapshots of ultrafast processes in atoms,[10,11] molecules,[12,13] and solid-state materials,[14,15,16,17] triggered by the strongfield interaction of the sample with an ultrashort few-cycle pulse. While this scheme is very convenient from the implementation viewpoint [carrier-envelope phase (CEP) stable few-cycle pulses are ideal drivers for the generation of isolated attosecond pulses, and a replica for excitation purposes can be derived] and grants exquisite temporal localization of the initially prepared excited wave packet due to the extremely short pulses employed, there are two main bottlenecks historically ascribed to this methodology, limiting the range of applications—on the one hand, the non-resonant and nonperturbative nature of the excitation process; on the other, the complications in data interpretation due to multiplet effects in probing inner valence states rather than genuine core level states (K and L edges)
We introduced a joint experimental and theoretical approach to follow in real-time the electronic structure change in molecules via attosecond transient absorption spectroscopy
Summary
Since the demonstration of attosecond pulses, in the extreme ultraviolet (XUV) region of the electromagnetic spectrum (10–124 eV), via high-order harmonic generation (HHG), these pulses have been exploited for time-resolved investigations of ultrafast photoinitiated processes in atoms, molecules, and solids. Scitation.org/journal/sdy been exploited to take snapshots of ultrafast processes in atoms,[10,11] molecules,[12,13] and solid-state materials,[14,15,16,17] triggered by the strongfield interaction of the sample with an ultrashort few-cycle pulse While this scheme is very convenient from the implementation viewpoint [carrier-envelope phase (CEP) stable few-cycle pulses are ideal drivers for the generation of isolated attosecond pulses, and a replica for excitation purposes can be derived] and grants exquisite temporal localization of the initially prepared excited wave packet due to the extremely short pulses employed, there are two main bottlenecks historically ascribed to this methodology, limiting the range of applications—on the one hand, the non-resonant and nonperturbative nature of the excitation process; on the other, the complications in data interpretation due to multiplet effects in probing inner valence states (usually M edges) rather than genuine core level states (K and L edges). That work assigned features based on conventional intuition known at the time; in hindsight from the new theoretical work here, numerous assignments of the features in the earlier experimental spectra are reassessed
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