Core-Hole Coherent Spectroscopy in Molecules.

We study the ultrafast dynamics initiated by a coherent superposition of core-excited states of nitrous oxide molecule. Using high-level ab initio methods, we show that the decoherence caused by the electronic decay and the nuclear dynamics is substantially slower than the induced ultrafast quantum beatings, allowing the system to undergo several oscillations before it dephases. We propose a proof-of-concept experiment using the harmonic up-conversion scheme available at x-ray free-electron laser facilities to trace the evolution of the created core-excited-state coherence through a time-resolved x-ray photoelectron spectroscopy.

Magnetic, Mechanically Interlocked Porphyrin-Carbon Nanotubes for Quantum Computation and Spintronics.

Atomic-scale reproducibility and tunability endorse magnetic molecules as candidates for spin qubits and spintronics. A major challenge is to implant those molecular spins into circuit geometries that may allow one, two, or a few spins to be addressed in a controlled way. Here, the formation of mechanically bonded, magnetic porphyrin dimeric rings around carbon nanotubes (mMINTs) is presented. The mechanical bond places the porphyrin magnetic cores in close contact with the carbon nanotube without disturbing their structures. A combination of spectroscopic techniques shows that the magnetic geometry of the dimers is preserved upon formation of the macrocycle and the mMINT. Moreover, the metallic core selection determines the spin location in the mMINT. The suitability of mMINTs as qubits is explored by measuring their quantum coherence times (Tm). Formation of the dimeric ring preserves the Tm found in the monomer, which remains in the µs scale for mMINTs. The carbon nanotube is used as vessel to place the molecules in complex circuits. This strategy can be extended to other families of magnetic molecules. The size and composition of the macrocycle can be tailored to modulate magnetic interactions between the cores and to introduce magnetic asymmetries (heterometallic dimers) for more complex molecule-based qubits.

Electronic Population Transfer via Impulsive Stimulated X-Ray Raman Scattering with Attosecond Soft-X-Ray Pulses.

Free-electron lasers provide a source of x-ray pulses short enough and intense enough to drive nonlinearities in molecular systems. Impulsive interactions driven by these x-ray pulses provide a way to create and probe valence electron motions with high temporal and spatial resolution. Observing these electronic motions is crucial to understand the role of electronic coherence in chemical processes. A simple nonlinear technique for probing electronic motion, impulsive stimulated x-ray Raman scattering (ISXRS), involves a single impulsive interaction to produce a coherent superposition of electronic states. We demonstrate electronic population transfer via ISXRS using broad bandwidth (5.5 eV full width at half maximum) attosecond x-ray pulses produced by the Linac Coherent Light Source. The impulsive excitation is resonantly enhanced by the oxygen 1s→2π^{*} resonance of nitric oxide (NO), and excited state neutral molecules are probed with a time-delayed UV laser pulse.

Tracking the Light-Induced Excited-State Dynamics and Structural Configurations of an Extraordinarily Long-Lived Metastable State at Room Temperature.

Time-resolved X-ray (Tr-XAS) and optical transient absorption (OTA) spectroscopy on the pico-microsecond timescale coupled with density functional theory calculations are applied to study the light-induced spin crossover processes of a Fe-based macrocyclic complex in solution. Tr-XAS analysis after light illumination shows the formation of a seven-coordinated high-spin quintet metastable state, which relaxes to a six-coordinated high-spin configuration before decaying to the ground state. Kinetic analysis of the macrocyclic complex reveals an unprecedented long-lived decay lifetime of approximately 42.6 µs. Comparative studies with a non-macrocyclic counterpart illustrate a significantly shortened approximately 568-fold decay lifetime of about 75 ns, and highlight the importance of the ligand arrangement in stabilizing the reactivity of the excited state. Lastly, OTA analysis shows the seven-coordinated high-spin state to be formed within approximately 6.2 ps. These findings provide a complete understanding of the spin crossover reaction and relaxation pathways of the macrocyclic complex, and reveal the importance of a flexible coordination environment for their rational design.

Symphony on strong field approximation.

This paper has been prepared by the Symphony collaboration (University of Warsaw, Uniwersytet Jagiellonski, DESY/CNR and ICFO) on the occasion of the 25th anniversary of the 'simple man's models' which underlie most of the phenomena that occur when intense ultrashort laser pulses interact with matter. The phenomena in question include high-harmonic generation (HHG), above-threshold ionization (ATI), and non-sequential multielectron ionization (NSMI). 'Simple man's models' provide both an intuitive basis for understanding the numerical solutions of the time-dependent Schrödinger equation and the motivation for the powerful analytic approximations generally known as the strong field approximation (SFA). In this paper we first review the SFA in the form developed by us in the last 25 years. In this approach the SFA is a method to solve the TDSE, in which the non-perturbative interactions are described by including continuum-continuum interactions in a systematic perturbation-like theory. In this review we focus on recent applications of the SFA to HHG, ATI and NSMI from multi-electron atoms and from multi-atom molecules. The main novel part of the presented theory concerns generalizations of the SFA to: (i) time-dependent treatment of two-electron atoms, allowing for studies of an interplay between electron impact ionization and resonant excitation with subsequent ionization; (ii) time-dependent treatment in the single active electron approximation of 'large' molecules and targets which are themselves undergoing dynamics during the HHG or ATI processes. In particular, we formulate the general expressions for the case of arbitrary molecules, combining input from quantum chemistry and quantum dynamics. We formulate also theory of time-dependent separable molecular potentials to model analytically the dynamics of realistic electronic wave packets for molecules in strong laser fields. We dedicate this work to the memory of Bertrand Carré, who passed away in March 2018 at the age of 60.

Optical anisotropy of non-perturbative high-order harmonic generation in gapless graphene.

High harmonic generation in atomic or molecular targets stands as a robust mechanism to produce coherent ultrashort pulses with controllable polarization in the extreme-ultraviolet. However, the production of elliptically or circularly-polarized harmonics is not straightforward, demanding complex combinations of elliptically or circularly-polarized drivers, or the use of molecular alignment techniques. Nevertheless, recent studies show the feasibility of high-harmonic generation in solids. In contrast with atoms and molecules, solids are high-density targets and therefore more efficient radiation sources. Among solid targets, 2D materials are of special interest due to their particular electronic structure, which conveys special optical properties. In this paper, we present theoretical calculations that demonstrate an extraordinary complex light-spin conversion in single-layer graphene irradiated at non perturbative intensities. Linearly-polarized drivings result in the emission of elliptically-polarized harmonics, and elliptically-polarized drivings may result in linearly-polarized or ellipticity-reversed harmonics. In addition, we demonstrate the ultrafast temporal modulation of the harmonic ellipticity.

Conservation of Torus-knot Angular Momentum in High-order Harmonic Generation.

High-order harmonic generation stands as a unique nonlinear optical up-conversion process, mediated by a laser-driven electron recollision mechanism, which has been shown to conserve energy, linear momentum, and spin and orbital angular momentum. Here, we present theoretical simulations that demonstrate that this process also conserves a mixture of the latter, the torus-knot angular momentum J_{γ}, by producing high-order harmonics with driving pulses that are invariant under coordinated rotations. We demonstrate that the charge J_{γ} of the emitted harmonics scales linearly with the harmonic order, and that this conservation law is imprinted onto the polarization distribution of the emitted spiral of attosecond pulses. We also demonstrate how the nonperturbative physics of high-order harmonic generation affect the torus-knot angular momentum of the harmonics, and we show that this configuration harnesses the spin selection rules to channel the full yield of each harmonic into a single mode of controllable orbital angular momentum.

Elucidating the Nature of the Excited State of a Heteroleptic Copper Photosensitizer by using Time-Resolved X-ray Absorption Spectroscopy.

We report the light-induced electronic and geometric changes taking place within a heteroleptic CuI photosensitizer, namely [(xant)Cu(Me2 phenPh2 )]PF6 (xant=xantphos, Me2 phenPh2 =bathocuproine), by time-resolved X-ray absorption spectroscopy in the ps-µs time regime. Time-resolved X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis enabled the elucidation of the electronic and structural configuration of the copper center in the excited state as well as its decay dynamics in different solvent conditions with and without triethylamine acting as a sacrificial electron donor. A three-fold decrease in the decay lifetime of the excited state is observed in the presence of triethylamine, showing the feasibility of the reductive quenching pathway in the latter case. A prominent pre-edge feature is observed in the XANES spectrum of the excited state upon metal to charge ligand transfer transition, showing an increased hybridization of the 3d states with the ligand p orbitals in the tetrahedron around the Cu center. EXAFS and density functional theory illustrate a significant shortening of the Cu-N and an elongation of the Cu-P bonds together with a decrease in the torsional angle between the xantphos and bathocuproine ligand. This study provides mechanistic time-resolved understanding for the development of improved heteroleptic CuI photosensitizers, which can be used for the light-driven production of hydrogen from water.

Electronic π-Delocalization Boosts Catalytic Water Oxidation by Cu(II) Molecular Catalysts Heterogenized on Graphene Sheets.

A molecular water oxidation catalyst based on the copper complex of general formula [(Lpy)CuII]2-, 22-, (Lpy is 4-pyrenyl-1,2-phenylenebis(oxamidate) ligand) has been rationally designed and prepared to support a more extended π-conjugation through its structure in contrast with its homologue, the [(L)CuII]2- water oxidation catalyst, 12- (L is o-phenylenebis(oxamidate)). The catalytic performance of both catalysts has been comparatively studied in homogeneous phase and in heterogeneous phase by π-stacking anchorage to graphene-based electrodes. In the homogeneous system, the electronic perturbation provided by the pyrene functionality translates into a 150 mV lower overpotential for 22- with respect to 12- and an impressive increase in the kcat from 6 to 128 s-1. Upon anchorage, π-stacking interactions with the graphene sheets provide further π-delocalization that improves the catalytic performance of both catalysts. In this sense, 22- turned out to be the most active catalyst due to the double influence of both the pyrene and the graphene, displaying an overpotential of 538 mV, a kcat of 540 s-1 and producing more than 5300 TONs.

Tracking the Structural and Electronic Configurations of a Cobalt Proton Reduction Catalyst in Water.

X-ray transient absorption spectroscopy (X-TAS) has been used to study the light-induced hydrogen evolution reaction catalyzed by a tetradentate macrocyclic cobalt complex with the formula [LCo(III)Cl2](+) (L = macrocyclic ligand), [Ru(bpy)3](2+) photosensitizer, and an equimolar mixture of sodium ascorbate/ascorbic acid electron donor in pure water. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analysis of a binary mixture of the octahedral Co(III) precatalyst and [Ru(bpy)3](2+) after illumination revealed in situ formation of a Co(II) intermediate with significantly distorted geometry and electron-transfer kinetics of 51 ns. On the other hand, X-TAS experiments of the complete photocatalytic system in the presence of the electron donor showed the formation of a square planar Co(I) intermediate species within a few nanoseconds, followed by its decay in the microsecond time scale. The Co(I) structural assignment is supported by calculations based on density functional theory (DFT). At longer reaction times, we observe the formation of the initial Co(III) species concomitant to the decay of Co(I), thus closing the catalytic cycle. The experimental X-ray absorption spectra of the molecular species formed along the catalytic cycle are modeled using a combination of molecular orbital DFT calculations (DFT-MO) and finite difference method (FDM). These findings allowed us to assign the full mechanistic pathway, followed by the catalyst as well as to determine the rate-limiting step of the process, which consists in the protonation of the Co(I) species. This study provides a complete kinetics scheme for the hydrogen evolution reaction by a cobalt catalyst, revealing unique information for the development of better catalysts for the reductive side of hydrogen fuel cells.

Sentinel Lymph Node Biopsy for Cutaneous Head and Neck Melanoma: Mapping the Parotid Gland.

BACKGROUND: Sentinel lymph node biopsy (SLNB) for primary cutaneous head and neck melanoma (CHNM) has been shown to be successful and is the current standard of care for intermediate-thickness melanoma. We evaluated our experience with CHNM associated with SLNB mapping to the region of the parotid gland. METHODS: Retrospective review of a prospectively collected melanoma database identified 1014 CHNMs. Two-hundred twenty-three patients underwent SLNB, and 72 (32%) had mapping in the region of the parotid gland between May 1995 and June 2003. RESULTS: The mean number of SLNs per patient was 2.5. A sentinel lymph node (SLN) was successfully identified in 94% of patients, and in 12%, the SLN was positive for metastatic disease. Biopsy of intraparotid SLNs was performed in 51.4% and of periparotid SLNs in 26.4%, and a superficial parotidectomy was performed in 22.2%. Ten patients were found to have lymph nodes in the parotid region with metastatic disease (eight identified by SLNB), and two (20%) patients developed intraparotid lymph node recurrence in the setting of a negative SLNB. Same-basin recurrence in SLN-negative patients was 3.3% with a median follow-up of 26 months. Facial nerve dysfunction was identified in seven (10%) patients. Facial nerve function returned to preoperative status in all patients. CONCLUSIONS: SLNB for patients with primary CHNM mapping to the parotid gland can be performed with a high degree of accuracy and a low morbidity consisting of temporary facial nerve paresis.

Nonperturbative Twist in the Generation of Extreme-Ultraviolet Vortex Beams.

High-order harmonic generation (HHG) has been recently proven to produce extreme-ultraviolet (XUV) vortices from the nonlinear conversion of infrared twisted beams. Previous works have demonstrated a linear scaling law of the vortex charge with the harmonic order. We demonstrate that this simple law hides an unexpectedly rich scenario for the buildup of orbital angular momentum (OAM) due to the nonperturbative behavior of HHG. The complexity of these twisted XUV beams appears only when HHG is driven by nonpure vortex modes, where the XUV OAM content is dramatically increased. We explore the underlying mechanisms for this diversity and derive a general conservation rule for the nonperturbative OAM buildup. The simple scaling found in previous works corresponds to the collapse of this scenario for the particular case of pure (single-mode) OAM driving fields.

Inner-shell photoionization and core-hole decay of Xe and XeF2.

Photoionization cross sections and partial ion yields of Xe and XeF2 from Xe 3d(5/2), Xe 3d(3/2), and F 1s subshells in the 660-740 eV range are compared to explore effects of the F ligands. The Xe 3d-ϵf continuum shape resonances dominate the photoionization cross sections of both the atom and molecule, but prominent resonances appear in the XeF2 cross section due to nominal excitation of Xe 3d and F 1s electrons to the lowest unoccupied molecular orbital (LUMO), a delocalized anti-bonding MO. Comparisons of the ion products from the atom and molecule following Xe 3d photoionization show that the charge-state distribution of Xe ions is shifted to lower charge states in the molecule along with production of energetic F(+) and F(2+) ions. This suggests that, in decay of a Xe 3d core hole, charge is redistributed to the F ligands and the system dissociates due to Coulomb repulsion. The ion products from excitation of the F 1s-LUMO resonance are different and show strong increases in the yields of Xe(+) and F(+) ions. The subshell ionization thresholds, the LUMO resonance energies, and their oscillator strengths are calculated by relativistic coupled-cluster methods and agree well with measurements.

Subcycle dynamics of excitons under strong laser fields.

Excitons play a key role in the linear optical response of two-dimensional (2D) materials. However, their role in the nonlinear response to intense, nonresonant, low-frequency light is often overlooked as strong fields are expected to tear the electron-hole pair apart. Using high-harmonic generation as a spectroscopic tool, we theoretically study their formation and role in the nonlinear optical response. We show that the excitonic contribution is prominent and that excitons remain stable even when the driving laser field surpasses the strength of the Coulomb field binding the electron-hole pair. We demonstrate a parallel between the behavior of strongly laser-driven excitons in 2D solids and strongly driven Rydberg states in atoms, including the mechanisms of their formation and stability. Last, we show how the excitonic contribution can be singled out by encapsulating the 2D material in a dielectric, tuning the excitonic energy and its contribution to the high-harmonic spectrum.

Attosecond impulsive stimulated X-ray Raman scattering in liquid water.

We report the measurement of impulsive stimulated x-ray Raman scattering in neutral liquid water. An attosecond pulse drives the excitations of an electronic wavepacket in water molecules. The process comprises two steps: a transition to core-excited states near the oxygen atoms accompanied by transition to valence-excited states. Thus, the wavepacket is impulsively created at a specific atomic site within a few hundred attoseconds through a nonlinear interaction between the water and the x-ray pulse. We observe this nonlinear signature in an intensity-dependent Stokes Raman sideband at 526 eV. Our measurements are supported by our state-of-the-art calculations based on the polarization response of water dimers in bulk solvation and propagation of attosecond x-ray pulses at liquid density.

Attosecond extreme ultraviolet vortices from high-order harmonic generation.

We present a theoretical study of high-order harmonic generation (HHG) and propagation driven by an infrared field carrying orbital angular momentum (OAM). Our calculations unveil the following relevant phenomena: extreme-ultraviolet harmonic vortices are generated and survive to the propagation effects, vortices transport high-OAM multiples of the corresponding OAM of the driving field and, finally, the different harmonic vortices are emitted with similar divergence. We also show the possibility of combining OAM and HHG phase locking to produce attosecond pulses with helical pulse structure.

Theoretical Approach for Electron Dynamics and Ultrafast Spectroscopy (EDUS).

In this manuscript, we present a theoretical framework and its numerical implementation to simulate the out-of-equilibrium electron dynamics induced by the interaction of ultrashort laser pulses in condensed-matter systems. Our approach is based on evolving in real time the density matrix of the system in reciprocal space. It considers excitonic and nonperturbative light-matter interactions. We show some relevant examples that illustrate the efficiency and flexibility of the approach to describe realistic ultrafast spectroscopy experiments. Our approach is suitable for modeling the promising and emerging ultrafast studies at the attosecond time scale that aim at capturing the electron dynamics and the dynamical electron-electron correlations via X-ray absorption spectroscopy.

Mapping the Ultrafast Mechanistic Pathways of Co Photocatalysts in Pure Water through Time-Resolved X-ray Spectroscopy.

Nanosecond time-resolved X-ray (tr-XAS) and optical transient absorption spectroscopy (OTA) are applied to study 3 multimolecular photocatalytic systems with [Ru(bpy)3 ]2+ photoabsorber, ascorbic acid electron donor and Co catalysts with methylene (1), hydroxomethylene (2) and methyl (3) amine substituents in pure water. OTA and tr-XAS of 1 and 2 show that the favored catalytic pathway involves reductive quenching of the excited photosensitizer and electron transfer to the catalyst to form a CoII square pyramidal intermediate with a bonded aqua molecule followed by a CoI square planar derivative that decays within ≈8 µs. By contrast, a CoI square pyramidal intermediate with a longer decay lifetime of ≈35 µs is formed from an analogous CoII geometry for 3 in H2 O. These results highlight the protonation of CoI to form the elusive hydride species to be the rate limiting step and show that the catalytic rate can be enhanced through hydrogen containing pendant amines that act as H-H bond formation proton relays.

Robotic-assisted left adrenal cystic mass excision in a pregnant patient.

A symptomatic adrenal mass diagnosed during pregnancy is a rare clinical scenario. Two primary considerations are the timing of intervention and determining the appropriate surgical approach. Here, we present the case of a young female patient with flank pain, whom on diagnostic imaging, was found to have a large cystic adrenal mass. She was taken for a robotic-assisted resection of her left-sided adrenal mass during the second trimester of pregnancy. Preoperative and postoperative assessment demonstrated a viable intrauterine pregnancy. She tolerated the procedure well and was discharged 5 days later with resolution of her symptoms on follow-up. As one of only three reported cases of robotic adrenal surgery during pregnancy, we demonstrate that a robotic-assisted surgical approach is a viable and durable surgical option under the given clinical circumstances.

Observation of site-selective chemical bond changes via ultrafast chemical shifts.

The concomitant motion of electrons and nuclei on the femtosecond time scale marks the fate of chemical and biological processes. Here we demonstrate the ability to initiate and track the ultrafast electron rearrangement and chemical bond breaking site-specifically in real time for the carbon monoxide diatomic molecule. We employ a local resonant x-ray pump at the oxygen atom and probe the chemical shifts of the carbon core-electron binding energy. We observe charge redistribution accompanying core-excitation followed by Auger decay, eventually leading to dissociation and hole trapping at one site of the molecule. The presented technique is general in nature with sensitivity to chemical environment changes including transient electronic excited state dynamics. This work provides a route to investigate energy and charge transport processes in more complex systems by tracking selective chemical bond changes on their natural timescale.