A5022034984- Spectroscopy and Quantum Chemical Studies
- Laser-Matter Interactions and Applications
- Molecular Junctions and Nanostructures
- Advanced Chemical Physics Studies
- Gold and Silver Nanoparticles Synthesis and Applications
- Plasmonic and Surface Plasmon Research
- Quantum and electron transport phenomena
- Advanced Fiber Laser Technologies
- Spectroscopy and Laser Applications
- Atomic and Molecular Physics
- Force Microscopy Techniques and Applications
- Mass Spectrometry Techniques and Applications
- Graphene research and applications
- Mechanical and Optical Resonators
- Quantum Information and Cryptography
- Quantum optics and atomic interactions
- Photochemistry and Electron Transfer Studies
- Cold Atom Physics and Bose-Einstein Condensates
- Quantum, superfluid, helium dynamics
- Electrochemical Analysis and Applications
- Optical Coatings and Gratings
- Advanced Thermodynamics and Statistical Mechanics
- Quantum Dots Synthesis And Properties
- Orbital Angular Momentum in Optics
- Laser Design and Applications
Northwestern University
2013-2022
Stanford University
2012-2016
SLAC National Accelerator Laboratory
2012-2016
Pulse Biosciences (United States)
2012
Arizona State University
2009
Institut de Recherche sur les Systèmes Atomiques et Moléculaires Complexes
2007
Université Toulouse III - Paul Sabatier
2007
Aarhus University
2006
Steacie Institute for Molecular Sciences
1995-2004
National Research Council Canada
1993-2002
We review the theoretical and experimental status of intense laser alignment---a field at interface between physics chemical dynamics with potential applications ranging from high harmonic generation nanoscale processing to stereodynamics control reactions. After placing approach in context other alignment techniques, we proceed a discussion underlying this technique description methods observing it laboratory. The roles played by frequency, pulse duration, system temperature are illustrated...
The rate of nonlinear ionization is strongly enhanced as a molecule stretched beyond its equilibrium internuclear separation, reaching peak that many orders magnitude greater than at either small or large distances. enhancement results from nonadiabatic electron localization near the nuclei and presence insensitive to laser frequency intensity. Most intense-field dissociative experiments are influenced by this effect.
A new method is suggested for the calculation of microcanonical cumulative reaction probability via flux autocorrelation relations. The Hamiltonian and operators are computed in a discrete variable representation (DVR) well-behaved Green’s operator, G(E+), obtained by imposing absorbing boundary conditions (ABC). Applications to one-dimensional-model problem collinear H+H2 show that DVR-ABC scheme provides very efficient direct probability, circumventing need compute state-to-state dynamics....
This is a review of some recent development in femtosecond filamentation science with emphasis on our collective work. Previously reviewed work the field will not be discussed. We thus start very brief description fundamental physics single powerful laser pulses air. Intensity clamping emphasized. One consequence that peak intensity inside one or more filaments would increase significantly even if focuses pulse at high power up to peta-watt level. Another clamped independent pressure....
An existence proof for single-molecule tip-enhanced Raman spectroscopy (SMTERS) is given using the frequency domain approach involving two isotopologues of Rhodamine 6G (R6G) that were previously employed surface-enhanced (SMSERS). A combination experimental and theoretical studies provides a detailed view isotopic response R6G–d0 R6G–d4 in 600 – 800 cm–1 region. The nature TERS experiment confirmed through lines evidence. First, vibrational signature only one isotopologue at time was...
The revival structure of strong-field-induced rotational wave packets differs qualitatively from structures analyzed in the past. One consequences this difference is strong enhancement alignment such after turn-off laser pulse, under field-free conditions.
We demonstrate, theoretically and experimentally, that an intense, elliptically polarized, nonresonant laser field can simultaneously force all three axes of a molecule to align along given fixed in space, thus inhibiting the free rotation Euler angles. Theoretically, effect is illustrated through time dependent quantum mechanical calculations. Experimentally, 3, 4-dibromothiophene molecules are aligned with nanosecond pulse. The alignment probed by 2D ion imaging fragments from 20 fs pulse...
Rotational excitation and spatial alignment in moderate intensity radiation fields are studied numerically analytically, using time-dependent quantum mechanics. Substantial rotational is found under conditions typically used time-resolved spectroscopy experiments. The broad wave packet excited by the laser pulse well defined conjugate angle space, peaking along field polarization direction. Both consequent can be controlled choice of parameters. Fragment angular distributions following weak...
The use of a discrete variable representation (DVR) and absorbing boundary conditions (ABC) to construct the outgoing Green’s function G(E+)≡limε→0(E+iε−H)−1, its subsequent determine cumulative reaction probability for chemical reaction, has been extended beyond our previous work [J. Chem. Phys. 96, 4412 (1992)] in several significant ways. In particular, present paper gives more thorough derivation analysis DVR-ABC approach, shows how same can be used obtain state-to-state (as well as...
Multiple vibrational modes have been observed for copper phthalocyanine (CuPc) adlayers on Ag(111) using ultrahigh vacuum (UHV) tip-enhanced Raman spectroscopy (TERS). Several important new experimental features are introduced in this work that significantly advance the state-of-the-art UHV-TERS. These include (1) concurrent sub-nm molecular resolution STM imaging Ag tips with laser illumination of tip-sample junction, (2) focusing and collection optics external to UHV-STM has two...
The cumulative reaction probability (CRP) (the Boltzmann average of which is the thermal rate constant) has been calculated for H2+OH↔H2O+H in its full (six) dimensionality total angular momentum J=0. calculation, should be (numerically) exact result assumed potential energy surface, was carried out by a direct procedure that avoids having to solve complete state-to-state reactive scattering problem. Higher momenta (J≳0) were taken into account approximately obtain constant k(T) over range...
This article reports the study of infrared plasmonics with both random and periodic arrays indium-tin-oxide (ITO) nanorods (NR). A description is given on synthesis, patterning, characterization physical properties ITO NR arrays. classical scattering model, along a 3-D finite-element-method finite-difference-time-domain numerical simulation method has been used to interpret unique light phenomena. It also shown that intrinsic plasma frequency can be varied through careful postsynthesis...
We demonstrate strong coupling between molecular excited states and surface plasmon modes of a slit array in thin metal film. The manifests itself as an anticrossing behavior the two newly formed polaritons. As strength grows, new mode emerges, which is attributed to long-range interactions mediated by plasmonic field. new, molecular-like repels polariton states, leads opening energy gaps both below above asymptotic free molecule energy.
Tip-enhanced Raman spectroscopy (TERS) provides chemical information for adsorbates with nanoscale spatial resolution, single-molecule sensitivity, and, when combined scanning tunneling microscopy (STM), Ångstrom-scale topographic resolution. Performing TERS under ultrahigh-vacuum conditions allows pristine and atomically smooth surfaces to be maintained, while liquid He cooling minimizes surface diffusion of across the solid surface, allowing direct STM imaging. Low-temperature TER (LT-TER)...
Tip-enhanced Raman spectroscopy (TERS) combines the ability of scanning probe microscopy (SPM) to resolve atomic-scale surface features with single-molecule chemical sensitivity surface-enhanced (SERS). Here, we report additional insights into nature conformational dynamics a free-base porphyrin at room temperature adsorbed on metal surface. We have interrogated switch between two metastable surface-mediated isomers meso-tetrakis(3,5-ditertiarybutylphenyl)-porphyrin (H2TBPP) Cu(111) At...
An explanation of the relative intensity fluctuations observed in single-molecule Raman experiments is described utilizing both tip-enhanced spectroscopy and time-dependent density functional theory calculations. No correlation mode to indicating that changes intensities are completely independent. Theoretical calculations provide convincing evidence not result diffusion, orientation, or local electromagnetic field gradients but rather subtle variations excited-state lifetime, energy,...
We present an approach to accurately construct the few-state model Hamiltonians for singlet fission processes on basis of ab initio electronic structure method tailored dimer wave functions, called active space decomposition strategy. In this method, molecular dimers is expressed in terms a linear combination products monomer states. apply tetracene and pentacene, using functions computed by restricted (RAS) method. Near-exact are π-electrons that contain up 7 × 1012 configurations. Our...
Nanoscale chemical imaging of a dynamic molecular phase boundary has broad implications for range problems in catalysis, surface science, and electronics. While scanning probe microscopy (SPM) is commonly used to study boundaries, its information content can be severely compromised by diffusion, irregular packing, or three-dimensional adsorbate geometry. Here, we demonstrate the simultaneous structural analysis...
The use of photoelectron angular distributions (PADs) as a probe in short-pulse, pump-probe scenarios is reviewed. We focus on concepts, the insight that can be gained through theoretical analysis, applications, and future opportunities. Time-resolved PADs are sensitive to both time-evolving rotational composition wavepackets their electronic symmetry. former feature renders this observable potential molecular structure, intensity effects, perturbations. latter PAD radiationless transitions.
The cumulative reaction probability is calculated for the H2+OH→H+H2O in its full (six) dimensionality total angular momentum J=0. calculation, which should give (numerically) exact result assumed potential energy surface, yields directly, without having to solve complete state-to-state reactive scattering problem. Higher momenta (J≳0) were taken into account approximately obtain thermal rate constant k(T) over range 300°<T<700°. deviates significantly from experimental...
We extend the concept of alignment by short intense pulses to dissipative environments within a density matrix formalism and illustrate application this method as probe properties dense media. In particular, we propose means disentangling rotational population relaxation from decoherence effects via strong laser alignment. also possibility suppressing prolong lifetime through choice field parameters. Implications several disciplines number potential applications are proposed.