A5018401865- Advanced Chemical Physics Studies
- Catalytic Processes in Materials Science
- Spectroscopy and Quantum Chemical Studies
- Laser-Matter Interactions and Applications
- Diamond and Carbon-based Materials Research
- Electron and X-Ray Spectroscopy Techniques
- Catalysis and Oxidation Reactions
- Advanced X-ray Imaging Techniques
- Molecular Junctions and Nanostructures
- Plant Water Relations and Carbon Dynamics
- Quantum, superfluid, helium dynamics
- Mass Spectrometry Techniques and Applications
- nanoparticles nucleation surface interactions
- Plant and animal studies
- Advanced Electron Microscopy Techniques and Applications
- Plant responses to elevated CO2
- Spectroscopy and Laser Applications
- TiO2 Photocatalysis and Solar Cells
- Mercury impact and mitigation studies
- Fire effects on concrete materials
- X-ray Spectroscopy and Fluorescence Analysis
- Laser Design and Applications
- Mechanical and Optical Resonators
- Surface and Thin Film Phenomena
- Solid State Laser Technologies
Chapman University
2016-2025
Fritz Haber Institute of the Max Planck Society
2017-2022
Orange (Poland)
2019
Interface (United States)
2015-2017
SLAC National Accelerator Laboratory
2013-2017
AlbaNova
2017
Stockholm University
2017
Stanford University
2015
University of California, Santa Barbara
2008-2011
Max Planck Society
2010-2011
Femtosecond x-ray laser pulses are used to probe the carbon monoxide (CO) oxidation reaction on ruthenium (Ru) initiated by an optical pulse. On a time scale of few hundred femtoseconds, pulse excites motions CO and oxygen (O) surface, allowing reactants collide, and, with transient close picosecond (ps), new electronic states appear in O K-edge absorption spectrum. Density functional theory calculations indicate that these result from changes adsorption site bond formation between...
We used the Linac Coherent Light Source free-electron x-ray laser to probe electronic structure of CO molecules as their chemisorption state on Ru(0001) changes upon exciting substrate by using a femtosecond optical pulse. observed that are consistent with weakening interaction but without notable desorption. A large fraction (30%) was trapped in transient precursor would precede calculated free energy molecule function desorption reaction coordinate density functional theory, including van...
Clean hydrogen production is highly desirable for future energy needs, making the understanding of molecular-level phenomena underlying photocatalytic both fundamentally and practically important. Water splitting on pure TiO2 inefficient, however, adding sacrificial methanol could significantly enhance photocatalyzed H2 production. Therefore, photochemistry at molecular level provide important insights to its activity. Here, we report first clear evidence derived from time-dependent...
Short intense laser pulses of visible and infrared light can dramatically accelerate crystal nucleation from transparent solutions; previous studies invoke mechanisms that are only applicable for ordered phases or high dielectric phases. However, we show similar induce CO(2) bubble in carbonated water. Additionally, water is cosupersaturated with argon glycine, bubbles escaping the without a laser. Our findings suggest possible link between laser-induced crystals.
We demonstrate the use of intense, quasi-half-cycle THz pulses, with an associated electric field component comparable to intramolecular fields, direct reaction coordinate a chemical by stimulating nuclear motions reactants. Using strong from pulse generated via coherent transition radiation ultrashort electron bunch, we present evidence that CO oxidation on Ru(0001) is selectively induced, while not promoting thermally induced desorption process. The initiated motion O atoms surface driven...
We describe how the unique temporal and spectral characteristics of X-ray free-electron lasers (XFEL) can be utilized to follow chemical transformations in heterogeneous catalysis real time. highlight systematic study CO oxidation on Ru(0 0 1), which we initiate either using a femtosecond pulse from an optical laser or by activating only oxygen atoms THz pulse. find that is promoted into entropy-controlled precursor state prior desorbing when surface heated absence oxygen, whereas presence...
All previous experimental and theoretical studies of molecular interactions at metal surfaces show that electronically nonadiabatic influences increase with velocity. We report the observation a electronic effect follows opposite trend: The probability electron emission from low–work function surface—Au(111) capped by half monolayer Cs—increases as velocity incident NO molecule decreases during collisions highly vibrationally excited NO(X 2 π ½ , V = 18; is vibrational quantum number NO),...
Tar is an undesirable byproduct of biomass gasification, which can be removed through catalytic reforming to syngas components. Iron a promising, abundant alternative highly active but toxic nickel catalysts. The results observed so far in studies with iron have been mixed. In this paper, the decomposition naphthalene, representative model compound tar, was studied on Fe(110) surface using temperature-programmed desorption (TPD), sum frequency generation spectroscopy (SFG), and X-ray...
Using visible and x-ray photoelectron spectroscopy, we measured the work function of a Au(111) surface at well-defined submonolayer coverage Cs. For Cs producing photoemission maximum with He-Ne laser, is 1.61+/-0.08 eV, consistent previous assumptions used to analyze vibrationally promoted electron emission. A discussion possible layer structures also presented.
Nanosecond optical pulses with high power and spectral brightness in the deep ultraviolet (UV) region have been produced by sum frequency mixing of nearly transform-limited-bandwidth IR light originating from a home-built injection-seeded ring cavity KTiOPO4 parametric oscillator (OPO) fourth harmonic beam an Nd:YAG laser used simultaneously to pump OPO second harmonic. We demonstrate UV output, tunable 204 207 nm, which exhibits pulse energies up 5 mJ bandwidth better than 0.01 cm−1....
We report the first direct measurement of kinetic energy exoelectrons produced by collisions vibrationally excited molecules with a low work function metal surface exhibiting electron excitations 64% (most probable) and 95% (maximum) initial vibrational energy. This remarkable efficiency for vibrational-to-electronic transfer is in good agreement previous results suggesting coupling multiple quanta to single electron.
We show that coadsorbed oxygen atoms have a dramatic influence on the CO desorption dynamics from Ru(0001). In contrast to precursor-mediated mechanism Ru(0001), presence of surface modifies electronic structure Ru such occurs predominantly via direct pathway. This phenomenon is directly observed in an ultrafast pump-probe experiment using soft x-ray free-electron laser monitor dynamic evolution valence species. supported with potential mean force along path obtained density-functional...
The concept of bonding and antibonding orbitals is fundamental in chemistry. population those the energetic difference between two reflect strength interaction. Weakening bond expected to reduce this splitting, but transient character bond-activation has so far prohibited direct experimental access. Here we apply time-resolved soft X-ray spectroscopy at a free-electron laser directly observe decreased bonding–antibonding splitting following using an ultrashort optical pulse.
We use a pump-probe scheme to measure the time evolution of C $K$-edge x-ray absorption spectrum from $\mathrm{CO}/\mathrm{Ru}(0001)$ after excitation by an ultrashort high-intensity optical laser pulse. Because short duration probe pulse and precise control delay, excitation-induced dynamics during first picosecond pump can be resolved with unprecedented resolution. By comparing density functional theory calculations, we find high internal stretch frustrated rotation modes occurring within...
The transient dynamics of carbon monoxide (CO) molecules on a Ru(0001) surface following femtosecond optical laser pump excitation has been studied by monitoring changes in the unoccupied electronic structure using an ultrafast X-ray free-electron (FEL) probe. particular symmetry perpendicularly chemisorbed CO is exploited to investigate how molecular orientation with time varying polarization FEL pulses. evolution spectral features corresponding desorption precursor state was well...
A surface femtosecond two-photon photoemission (2PPE) spectrometer devoted to the study of ultrafast excited electron dynamics and photochemical kinetics on metal oxide surfaces has been constructed. Low energy photoelectrons are measured using a hemispherical analyzer with an imaging detector that allows us detect angular distributions simultaneously. Mach–Zehnder interferometer was built for time-resolved 2PPE (TR-2PPE) measurement dynamics, which demonstrated Cu(111) surface. scheme...
We report kinetic energy distributions of exoelectrons produced by collisions highly vibrationally excited NO molecules with a low work function Cs dosed Au(111) surface. These measurements show that dissipation pathways involving nonadiabatic conversion vibrational to electronic can result in excitation more than 3 eV, consistent the available energy. measured dependence electron on translational and incident find clear positive correlation between final initial weak but observable inverse...
A mass spectrometric investigation has been made of the angular number distributions KCl and K2Cl2 molecules effusing from cylindrical orifices with geometries L/R = 1−4 at temperatures 565, 585, 605°C. It was found that for neither nor molecule agrees predictions classical Clausing model. The distribution monomer is more diffuse than predicted by theory, whereas dimer highly focused experimental or theoretical distribution. For a given orifice geometry, progressive defocusing both beams...
The direct elucidation of the reaction pathways in heterogeneous catalysis has been challenging due to short-lived nature intermediates. Here, we directly measured on ultrafast time scales initial hydrogenation steps adsorbed CO a Ru catalyst surface, which is known as bottleneck syngas and CO2 reforming processes. We initiated with an laser temperature jump probed transient changes electronic structure using real-time X-ray spectroscopy. In combination theoretical simulations, verified...
We report on carbon monoxide desorption and oxidation induced by 400 nm femtosecond laser excitation the O/Ru(0001) surface probed time-resolved x-ray absorption spectroscopy (TR-XAS) at K-edge. The experiments were performed under constant background pressures of CO (6 × 10-8 Torr) O2 (3 Torr). Under these conditions, we detect two transient species with narrow 2π* peaks, suggesting little interaction surface. Based polarization measurements, find that have opposing orientations: (1)...
Diffuse light has been shown to alter plant leaf photosynthesis, transpiration and water-use efficiency. Despite this, the angular distribution of for artificial sources used with common gas exchange systems is unknown. Here, we quantify from demonstrate use an integrating sphere manipulating those distributions. Among three different systems, a 90° angle perpendicular surface (±5.75°) was <25% total reaching surface. The resulted in greater range possible distributions predominantly direct...
Methanol decomposition on Ni(111) surfaces has been studied in the presence and absence of oxygen using temperature-programmed desorption temperature-dependent sum frequency generation spectroscopy. Under both conditions C-H O-H bonds break, forming carbon monoxide atomic hydrogen surface. No C-O bond scission was observed, limiting number reaction pathways. The break first (>150 K), surface methoxy, followed by breakage (>250 K). All desorbs from as H2 through H+H recombinative desorption....
We report on atom-specific activation of CO oxidation Ru(0001) via resonant X-ray excitation. show that 1s core-level excitation atomically adsorbed oxygen in the co-adsorbed phase and directly drives oxidation. separate this direct channel from indirectly driven induced substrate heating. Based density functional theory calculations, we identify valence-excited state created by Auger decay as driving electronic for utilized fresh-slice multi-pulse mode at Linac Coherent Light Source...