Real-time observation of ultrafast X-ray induced electron and nuclear dynamics in molecules

Observing electron and nuclear rearrangements in real-time at specific atoms and without perturbing the system poses a great challenge. Such an achievement is becoming a reality thanks to the capacitites of X-ray Free Electron Lasers of generating ultrashort and intense x-ray pulses. X-ray photons interact mainly with core electrons, whose binding energy is both element-specific and sensitive to the local chemical environment. In order to disentangle the x-ray induced dynamics, we developed quantum models that treat both electron and nuclear motions. Using these tools, we interpret the first Impulsive Stimulated X-ray Raman Scattering experiment in a molecule, nitric oxide, which uses an intense soft x-ray attosecond pulse to induce electronic population transfer and generates a local electronic wavepacket. We also show the possibility to induce selective bond breaking and hydrogen migration in formamide using a two-color x-ray femtosecond pump-probe sequence. Using a similar scheme, we correlate the ultrafast dynamics arising from purely electronic excitation to the local chemical shifts in carbon monoxide. We follow in real-time charge-redistribution accompanying the population transfer from a core-excited state to relaxation via Auger decay, leading ultimately to dissociation and hole trapping at one site of the molecule. Our studies shed light on the most fundamental ultrafast processes taking place in matter, both in linear and nonlinear regimes.