Abstract
Attosecond X-ray pulses are short enough to capture snapshots of molecules undergoing nonadiabatic electron and nuclear dynamics at conical intersections (CoIns). We show that a stimulated Raman probe induced by a combination of an attosecond and a femtosecond pulse has a unique temporal and spectral resolution for probing the nonadiabatic dynamics and detecting the ultrafast (∼4.5 fs) passage through a CoIn. This is demonstrated by a multiconfigurational self-consistent-field study of the dynamics and spectroscopy of the furan ring-opening reaction. Trajectories generated by surface hopping simulations were used to predict Attosecond Stimulated X-ray Raman Spectroscopy signals at reactant and product structures as well as representative snapshots along the conical intersection seam. The signals are highly sensitive to the changes in nonadiabatically coupled electronic structure and geometry.
Highlights
The ultrafast electron and nuclear dynamics through conical intersections (CoIns)
Trajectories were generated by surface hopping nonadiabatic molecular dynamics (MD) simulations, and Attosecond Stimulated X-ray Raman Spectroscopy (ASRS) signals were calculated at selected snapshots
To set the stage for the ASRS signals of the nonadiabatic dynamics of a complex molecular system, i.e., the ring opening reaction of furan, we first illustrate the power of the technique with help of a simple model (see scheme in Fig. 2(e)) that captures the essentials of CoIn-mediated relaxation processes. 4 valence states, g, e; e2, and e3, are coupled to 2 core excited states, f and f2
Summary
The ultrafast electron and nuclear dynamics through CoIn. Attosecond pulses are produced by high harmonic tabletop sources, and much brighter femtosecond X-ray pulses are made possible by free electron lasers.. We assumed that the electronic Hamiltonian does not change considerably during the fast interaction with the Raman probe (i.e., we neglect the dynamics during the interaction of the attosecond pulse). This is justified, since the X-ray Raman process occurs within the core lifetime ð$ 5 fsÞ, whereby the nuclear motions are frozen. We show that ASRS captures the geometrical and electronic structure changes when a CoIn is reached and passed, and can discriminate reactant, product, and CoIns with high sensitivity This is confirmed by a complete active space self-consistent-field (CASSCF) spectroscopic study of the dynamics and relaxation pathways in the ring opening of photoexcited furan. Trajectories were generated by surface hopping nonadiabatic molecular dynamics (MD) simulations, and ASRS signals were calculated at selected snapshots
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