Ultrafast dynamics in polymeric carbon nitride thin films probed by time-resolved EUV photoemission and UV-Vis transient absorption spectroscopy.

The ground- and excited-state electronic structures of four polymeric carbon nitride (PCN) materials have been investigated using a combination of photoemission and optical absorption spectroscopy. To establish the driving forces for photocatalytic water-splitting reactions, the ground-state data was used to produce a band diagram of the PCN materials and the triethanolamine electron scavenger, commonly implemented in water-splitting devices. The ultrafast charge-carrier dynamics of the same PCN materials were also investigated using two femtosecond-time-resolved pump-probe techniques: extreme-ultraviolet (EUV) photoemission and ultraviolet-visible (UV-Vis) transient absorption spectroscopy.

Ultrafast kinetics of linkage isomerism in Na[Fe(CN)NO] aqueous solution revealed by time-resolved photoelectron spectroscopy.

The kinetics of ultrafast photoinduced structural changes in linkage isomers is investigated using Na[Fe(CN)NO] as a model complex. The buildup of the metastable side-on configuration of the NO ligand, as well as the electronic energy levels of ground, excited, and metastable states, has been revealed by means of time-resolved extreme UV (XUV) photoelectron spectroscopy in aqueous solution, aided by theoretical calculations. Evidence of a short-lived intermediate state in the isomerization process and its nature are discussed, finding that the complete isomerization process occurs in less than 240 fs after photoexcitation.

Light-induced relaxation dynamics of the ferricyanide ion revisited by ultrafast XUV photoelectron spectroscopy.

Photoinduced charge transfer in transition-metal coordination complexes plays a prominent role in photosynthesis and is fundamental for light-harvesting processes in catalytic materials. However, revealing the relaxation pathways of charge separation remains a very challenging task because of the complexity of relaxation channels and ultrashort time scales. Here, we employ ultrafast XUV photoemission spectroscopy to monitor fine mechanistic details of the electron dynamics following optical ligand-to-metal charge-transfer excitation of ferricyanide in aqueous solution.

Ultrafast Spin Crossover in [Fe (bpy) ] : Revealing Two Competing Mechanisms by Extreme Ultraviolet Photoemission Spectroscopy.

Photoinduced spin-flip in Fe complexes is an ultrafast phenomenon that has the potential to become an alternative to conventional processing and magnetic storage of information. Following the initial excitation by visible light into the singlet metal-to-ligand charge-transfer state, the electronic transition to the high-spin quintet state may undergo different pathways. Here we apply ultrafast XUV (extreme ultraviolet) photoemission spectroscopy to track the low-to-high spin dynamics in the aqueous iron tris-bipyridine complex, [Fe(bpy) ] , by monitoring the transient electron density distribution among excited states with femtosecond time resolution.

Ultrafast excited states dynamics of [Ru(bpy)] dissolved in ionic liquids.

Room-temperature ionic liquids (ILs) represent a well-known class of materials exhibiting extremely low vapor pressures and high electrochemical stability. These properties make ILs attractive for various applications requiring UHV conditions. Here, we apply 1-ethyl-3-methylimidazolium trifluoromethanesulfonate [EMIM][TfO] as a solvent to investigate the excited state dynamics of the transition metal complex [Ru(bpy)] with the use of ultrafast XUV photoelectron spectroscopy.

Charge Transfer Dynamics at Dye-Sensitized ZnO and TiO2 Interfaces Studied by Ultrafast XUV Photoelectron Spectroscopy.

Interfacial charge transfer from photoexcited ruthenium-based N3 dye molecules into ZnO thin films received controversial interpretations. To identify the physical origin for the delayed electron transfer in ZnO compared to TiO2, we probe directly the electronic structure at both dye-semiconductor interfaces by applying ultrafast XUV photoemission spectroscopy. In the range of pump-probe time delays between 0.

Charge transfer to solvent dynamics in iodide aqueous solution studied at ionization threshold.

We explore the early-time electronic relaxation in NaI aqueous solution exposed to a short UV laser pulse. Rather than initiating the charge transfer reaction by resonant photoexcitation of iodide, in the present time-resolved photoelectron spectroscopy study the charge-transfer-to-solvent (CTTS) states are populated via electronic excitation above the vacuum level. By analyzing the temporal evolution of electron yields from ionization of two transient species, assigned to CTTS and its first excited state, we determine both their ultrafast population and relaxation dynamics.

Monochromatization of femtosecond XUV light pulses with the use of reflection zone plates.

We report on a newly built laser-based tabletop setup which enables generation of femtosecond light pulses in the XUV range employing the process of high-order harmonic generation (HHG) in a gas medium. The spatial, spectral, and temporal characteristics of the XUV beam are presented. Monochromatization of XUV light with minimum temporal pulse distortion is the central issue of this work.

Time-of-flight electron spectrometer for a broad range of kinetic energies.

A newly constructed time-of-flight electron spectrometer of the magnetic bottle type is characterized for electron detection in a broad range of kinetic energies. The instrument is designed to measure the energy spectra of electrons generated from liquids excited by strong laser fields and photons in the range of extreme ultra violet and soft X-rays. Argon inner shell electrons were recorded to calibrate the spectrometer and investigate its characteristics, such as energy resolution and collection efficiency.

Threshold photodetachment in a repulsive potential.

We report on the first experimental observation of a new threshold behavior observed in the 5(2)G partial channel in photodetachment of K(-). It arises from the repulsive polarization interaction between the detached electron and the residual K(5(2)G) atom, which has a large negative dipole polarizability. In order to account for the observation in the K(5(2)G) channel, we have developed a semiclassical model that predicts an exponential energy dependence for the cross section.

Electron rescattering in above-threshold photodetachment of negative ions.

We present experimental and theoretical results on photodetachment of Br(-) and F(-) in a strong infrared laser field. The observed photoelectron spectra of Br(-) exhibit a high-energy plateau along the laser polarization direction, which is identified as being due to the rescattering effect. The shape and the extension of the plateau is found to be influenced by the depletion of negative ions during the interaction with the laser pulse.

Two-electron photodetachment of negative ions in a strong laser field.

We study the photodetachment of H-, F-, and Br- in a short laser pulse of 800 nm wavelength and 6 x 10(14) W/cm2 peak intensity. Photoelectron spectra, recorded with the use of an imaging technique, reveal a substantial contribution from the sequential process of double detachment of halogen negative ions. The saturation effect is shown to play a crucial role in this process.

Experimental study of photodetachment in a strong laser field of circular polarization.

Negative fluorine ions are exposed to a circularly polarized infrared laser pulse with a peak intensity on the order of 2.6 x 10(13) W/cm(2). A fundamental difference, as compared to the case of linearly polarized field, is found in the absence of any structure in the photoelectron spectrum that can be associated with the quantum interference effect.

Production of energetic electrons in the process of photodetachment of F-.

An imaging technique is used to record an energy and angle resolved spectrum of electrons produced by photodetachment of F- in a strong infrared laser pulse. The spectrum involves contributions from more than 23 excess photon detachment channels. Its higher energy part extends beyond the classical cutoff value, and it appears as a pronounced plateau localized within a small angle along the laser polarization axis.

Photodetachment of H- in a strong infrared laser field.

Negative hydrogen ions are exposed to a short infrared laser pulse of 2.15 microm wavelength and 250 fs duration. An imaging technique is used to record the energy resolved angular distribution of photoelectrons.

Spectrum of doubly excited states in the K- ion.

The energies and widths of doubly excited states of the K- ion in the vicinity of the K(5 2D,7 2S,5 2F) thresholds have been measured in high resolution using a sensitive collinear laser-ion beam apparatus. These transient states appeared as resonances in the partial cross section for photodetachment via the K(5 2S)+e(-)(epsilon(p)) channel. Series of two states below the 5 2D threshold and four states below the 5 2F threshold have been found.

Autodetachment of doubly excited states in nonhydrogenic negative ions.

A semiclassical model is developed to describe the two-electron dynamics of the process of autodetachment. A formula derived for the partial width of a doubly excited state represents a product of an amplitude and phase factors. An anomalous width behavior is predicted for states near a threshold when the orbital angular momentum of the outer electron is high.