Many photoinduced processes including photosynthesis and human vision happen in organic molecules and involve coupled femtosecond dynamics of nuclei and electrons. Organic molecules with heteroatoms often possess an important excited-state relaxation channel from an optically allowed ππ* to a dark nπ* state. The ππ*/nπ* internal conversion is difficult to investigate, as most spectroscopic methods are not exclusively sensitive to changes in the excited-state electronic structure. Here, we report achieving the required sensitivity by exploiting the element and site specificity of near-edge soft X-ray absorption spectroscopy. As a hole forms in the n orbital during ππ*/nπ* internal conversion, the absorption spectrum at the heteroatom K-edge exhibits an additional resonance. We demonstrate the concept using the nucleobase thymine at the oxygen K-edge, and unambiguously show that ππ*/nπ* internal conversion takes place within (60 ± 30) fs. High-level-coupled cluster calculations confirm the method’s impressive electronic structure sensitivity for excited-state investigations.

The quantum mechanical motion of electrons in molecules and solids occurs on the sub-femtosecond timescale. Consequently, the study of ultrafast electronic phenomena requires the generation of laser pulses shorter than 1 fs and of sufficient intensity to interact with their target with high probability.Probing these dynamics with atomic-site specificity requires the extension of sub-femtosecond pulses to the soft X-ray spectral region. Here we report the generation of isolated GW-scale soft X-ray attosecond pulses with an X-ray free-electron laser. Our source has a pulse energy that is six orders of magnitude larger than any other source of isolated attosecond pulses in the soft X-ray spectral region, with a peak power in the tens of gigawatts. This unique combination of high intensity, high photon energy and short pulse duration enables the investigation of electron dynamics with X-ray non-linear spectroscopy and single-particle imaging.their assistance in designing, constructing and installing the XLEAP wiggler. We also acknowledge the SLAC Accelerator Operations group, and the Mechanical and Electrical engineering divisions of the SLAC Accelerator Directorate, especially

Unveiling the nature of the bosonic excitations that mediate the formation of Cooper pairs is a key issue for understanding unconventional superconductivity. A fundamental step toward this goal would be to identify the relative weight of the electronic and phononic contributions to the overall frequency (Ω) dependent bosonic function, Π(Ω). We perform optical spectroscopy on Bi2Sr2Ca0.92Y0.08Cu2O 8+δ crystals with simultaneous time-and frequency-resolution; this technique allows us to disentangle the electronic and phononic contributions by their different temporal evolution. The strength of the interaction (λ∼1.1) with the electronic excitations and their spectral distribution fully account for the high critical temperature of the superconducting phase transition. [7]. Inelastic neutron and X-ray scattering experiments found evidence for both QP-phonon anomalies [8] and bosonic excitations attributed to spin fluctuations [7,9] and loop currents [10]. Dip features in tunnelling experiments have been used to alternatively support the scenarios of dominant electron-phonon interactions [11] or antiferromagnetic spin fluctuations [12]. The frequency-dependent dissipation of the Drude optical conductivity, σ (ω), measured by equilibrium optical spectroscopies, has been interpreted [13][14][15] as the coupling of electrons to bosonic excitations, in which the separation of the phononic and electronic contributions is impeded by their partial coexistence on the same energy scale (<90 meV).We disentangle the electronic and phononic contributions to Π(Ω) through a non-equilibrium optical spectroscopy, in which the femtosecond time-resolution is combined with an energy-resolution smaller than 10 meV, over a wide photon energy range (0.5-2 eV). Our approach is based on the widely-used assumption [16,17] that, after the interaction between a superconductor and a short laser pulse (1.55 eV photon energy), the effective electronic temperature (T e ) relaxes toward its equilibrium value through energy exchange with the different degrees of freedom that linearly contribute to Π(Ω). In a more formal description, the total bosonic function is given by Π(Ω)=Π be (Ω)+Π SCP (Ω)+Π lat (Ω) where Π be refers to the bosonic excitations of electronic origin at the effective temperature T be , Π SCP to the small fraction of strongly-coupled phonons (SCPs) at T SCP [16] and Π lat to all other * Electronic address: s.f.p.dalconte@tue.nl † Electronic address: claudio.giannetti@unicatt.it

Elementary processes associated with ionization of liquid water provide a framework for understanding radiation-matter interactions in chemistry and biology. Although numerous studies have been conducted on the dynamics of the hydrated electron, its partner arising from ionization of liquid water, H2O+, remains elusive. We used tunable femtosecond soft x-ray pulses from an x-ray free electron laser to reveal the dynamics of the valence hole created by strong-field ionization and to track the primary proton transfer reaction giving rise to the formation of OH. The isolated resonance associated with the valence hole (H2O+/OH) enabled straightforward detection. Molecular dynamics simulations revealed that the x-ray spectra are sensitive to structural dynamics at the ionization site. We found signatures of hydrated-electron dynamics in the x-ray spectrum.