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Physical Sciences

Frontiers in Chemical Physics & Analysis

2016

Theofanis Kitsopoulos
Theofanis Kitsopoulos

"CO Oxidation on Pt(111): Deciphering the Second Mechanism Using Slice Imaging"

Max Planck Institute for Biophysical Chemistry
Thursday, July 28, 2016
EMSL Boardroom
2:00 PM

2013

"Screening of Charged Electrodes by Ionic Liquids: A Simulation Study"

Professor, Department of Chemistry
University of Cambridge, UK
Thursday, September 5, 2013
EMSL Auditorium
10:00AM

Near a solid wall ionic liquids are layers. If the walls are charged, layers of cations and anions tend to separate, due to electrostatic forces. Although the average charge density is zero in the bulk of the liquid, near the walls there are large oscillations in the charge density and potential as a function of distance from the wall. There is significant overcompensation of the wall charge by the first liquid layer, which is reversed in the second layer. Measurements of free energy profiles show that charged solutes prefer to embed themselves in layers of the same charge, replacing ionic liquid ions. This results in high free energy barriers impeding the passage of charged solutes to the electrode, which may slow electrode reactions. We investigated the local environment of solute ions in regions of maximum and minimum free energy.


"Biominerals and Their Formation Mechanisms"

Professor, Department of Physics
University of Wisconsin-Madison
Tuesday, July 30, 2013
EMSL Auditorium
9:00AM

Carbonate biominerals are among the most interesting materials on Earth. They play a major role in the CO2 cycle, buffer acidifying oceans, and master templation, self-assembly, nanofabrication, phase transitions, space filling, crystal nucleation and growth mechanisms. An imaging modality, introduced in the last 6 years, enables direct observation of the orientation of carbonate crystals, at the nano- and micro-scale, and the interesting patterns they form. This is Polarization-dependent Imaging Contrast (PIC) mapping, which is based on X-ray linear dichroism, and uses PhotoElectron Emission spectroMicroscopy.
I will discuss PIC-mapping results from biominerals, including mollusk shells, sea urchin teeth, and ascidian spicules, and show that these led to fundamental discoveries on the formation mechanisms of biominerals.


2012

"Aqueous Solvation in Extreme Conditions: Accurate Calculations when Accurate Measurements are not Possible"

Welch Professor, Department of Chemistry & Biochemistry
Texas Tech University
Tuesday, November 6, 2012
BSF Crick
10:00AM

Direct dynamics have made the application of classical chemical dynamics simulations possible for a broad range of problems. However, since classical dynamics is approximate it is important to understand when the use of classical dynamics is appropriate. In this talk the following will be addressed: (1) the methodology of direct dynamics simulations; (2) accuracy of classical dynamics simulations, with emphasis on unimolecular and intramolecular dynamics; (3) post-transition state dynamics; and (4) gas-phase SN2 reaction dynamics. The VENUS/NWChem software package is used for the simulations and access to high-performance computing is critical for the research.


"It's All About Energy!. The Impact of Theory and Computation"

Professor, Chemistry and Physics
University of California-Davis
Tuesday, September 25, 2012
EMSL Auditorium
10:00AM

Professor Galli will discuss problems involved in understanding and controlling energy conversion processes, including photo-electrochemical and thermoelectric conversion. Using recent examples from ab initio and atomistic simulations done by her and her team at the University of California-Davis, she will discuss two intertwined issues:

  • What is the impact of theory and computation?
  • How do we take up the challenge of building much needed tighter connections between theory and experiment?

Professor Michael Gillan

Professor Michael Gillan

"Water on a Knife-Edge: The Subtle Balance of Forces in Clusters, Ice and Liquid"

London Centre for Nanotechnology & Thomas Young Centre
University College London, UK
Friday, April 27, 2012
EMSL Auditorium
9:30AM

Water has probably been studied more comprehensively than any other substance, but its molecular-scale energetics remains surprisingly elusive. Parameterized interaction models, including some developed at PNNL, can be remarkably successful. But widely used electronic-structure methods based on conventional density-functional theory (DFT) struggle to reproduce the properties of water clusters, ice structures and the bulk liquid, for reasons that are still controversial. I will summarize some new approaches that we are pursuing at UCL in collaboration with colleagues at Cambridge and Bristol, focusing particularly on our recent work with quantum Monte Carlo (QMC) [1] and Gaussian Approximation Potentials (GAP) [2]. I will show that QMC is much more accurate than DFT for the energetics of clusters [3] and ice structures [4], and that it can also supply useful benchmarks for statistical samples of configurations of the bulk liquid. We are using QMC and correlated quantum chemistry techniques to analyze the sources of error in DFT approximations and to quantify the accuracy of GAP corrections to DFT. It is becoming clear from this work that conventional DFTs have a hard time describing water systems because they misrepresent the subtle balance between 2-body (dispersion) and beyond-2-body (polarization) parts of the energy.


Professor Geoff Thornton

Professor Geoff Thornton

"Influence of Wet Electron States on the Water-Oxygen Surface Chemistry of TiO2."

London Centre for Nanotechnology & Thomas Young Centre
University College London, UK
Wednesday, April 25, 2012
EMSL Auditorium
11:00AM

Oxygen vacancies on metal oxide surfaces have long been thought to play a key role in the surface chemistry. For the (110) surface of TiO2, this view was recently challenged by work which suggested that a quasiparticle bandgap state involved in the reactivity arises from near-surface Ti interstials. Here I describe some recent experiments that tested this idea. We find that vacancies provide the dominant contribution to the band gap state. As for the reaction with molecules, such processes have been directly visualised in the case of the model photocatalyst surface TiO2(110) in reactions with water and dioxygen. These vacancies have been assumed to be neutral in calculations of the surface properties. However, by comparing experimental and simulated scanning tunneling microscopy images and spectra, we show that oxygen vacancies act as trapping centres and are negatively charged. We demonstrate that charging the defect significantly affects the reactivity by following the reaction of dioxygen with surface hydroxyl formed by water dissociation at the vacancies. Calculations with charged hydroxyl favour a condensation reaction forming water and surface oxygen adatoms, in line with experimental observations. This contrasts with simulations using neutral hydroxyl where hydrogen peroxide is found to be the most stable product. An interesting question remains as to the relevance of these results to the liquid water—TiO2 interface. Surface X-ray diffraction measurements after dipping the (110) surface in water reveal that the surface is hydroxylated in the first layer of the interface, with ordering of water in the second layer. This is in contrast to the results of recent calculations of the perfect surface, which suggest no dissociation at the liquid/TiO2(110) interface.


David Manolopoulo

Professor David Manolopoulos

"Competing Quantum Effects in Liquid Water"

Physical and Theoretical Chemistry Laboratory
The University of Oxford
Tuesday, March 20, 2012
EMSL Auditorium
9:00AM

I will begin this talk with a brief review of the ring polymer molecular dynamics (RPMD) method for condensed phase quantum dynamics. I will then use this method to investigate the properties of a flexible water model that has been parameterized to agree with a wide variety of experimental measurements in quantum mechanical (path integral) simulations. I shall show in particular that there is a competition between two opposing quantum mechanical effects in the dynamics of the room temperature liquid. The zero point motion in the intramolecular OH stretch increases the average OH bond length and the average dipole moment of the water molecules, leading to stronger intermolecular interactions and a more viscous liquid. However, this is offset by the zero point motion in the intermolecular modes, which disrupts the hydrogen bonding network and makes the liquid more labile again. The net result is that there is only a very small overall quantum mechanical effect in the self-diffusion and orientational relaxation of the liquid. If time permits at the end of the talk, I shall go on to discuss some related studies by other groups that support this picture.


Art Placeholder

Professor Takayuki Ebata

"Laser Spectroscopic and Theoretical Study of Encapsulation Complexes in the Gas Phase Toward Molecular Level Understanding of the Encapsulation Mechanism of Host-Guest Complexes"

Department of Chemistry
Graduate School of Science Hiroshima University, Japan
Thursday, March 1, 2012
EMSL Auditorium
11:00AM

Laser spectroscopic and theoretical study will be presented for elucidating the structures and complexation mechanism of gas phase host-guest complexes formed in supersonic jets and electrospray ionization cold 22 ion-trap. The examined hosts include crown ethers and calix[4]arene, and for the guest species various neutral molecules and alkali metal cations are chosen. We measure the electronic spectra by laser-induced fluorescence (LIF), mass-selected resonance enhanced multiphoton ionization (REMPI) and ultraviolet-ultraviolet hole-burning (UV-UV HB) spectroscopy. The vibrational spectra are measured by infrared-ultraviolet double resonance (IR-UV DR) and fragment detected infrared photodissociation (IRPD) spectroscopy. For the ionic complexes, ultraviolet photodissociation (UVPD) and IR-UV DR spectroscopy has been applied. The obtained results are analyzed by density functional theory and first principles electronic structure calculations. We discuss how the host molecule changes its conformation or which conformer is preferred for forming stable encapsulation complex as well as the key interactions, leading to the molecular recognition.


Michiel Sprik
Michiel Sprik

Professor Michiel Sprik

"Density Functional Theory Modeling of the Metal Oxide Water Interface"

Department of Chemistry
University of Cambridge
Monday, February 27, 2012
EMSL Auditorium
10:00AM

The interface between a metal oxide and an aqueous solution is a complex environment controlled by the exchange of charge between solid and electrolyte. Coordination with the positive metal ions increases the acidity of adsorbed water which at high pH leads to deprotonation and the buildup of negative charge. Alternatively basic oxygen sites on the surface can become protonated at low pH. Metal oxides can also exchange electronic charge with the electrolyte if the metal ions are redox active. Examples are transition metal ions. Modeling these processes is a major challenge for electronic structure calculation. In this talk, Professor Sprik will outline the DFT-based molecular dynamics methodology that was developed to meet this challenge using the calculation of the pH of zero proton charge, the potential at zero electronic charge and electric double layer capacitance of a small set of structurally related semiconductor oxides as validation. The key tool in the approach is a scheme for a molecular dynamics normal hydrogen electrode. As an application, Professor Sprik will discuss the thermochemistry of the creation of hydroxyl radicals at the TiO2/water interface. All these calculations have been carried out using the CP2K package. The recent implementation of efficient methods for the evaluation of exact exchange in extended systems has been in particular critical for the application to semiconductor oxides as reported in this talk.


Klaus Müller-Dethlefs
Klaus Müller-Dethlefs

Professor Klaus Müller-Dethlefs

"A Novel Ultra-Cold Quantum Plasma: From Wigner Crystallization to a Molecular Bose-Einstein Condensate?"

Founding Director of The Photon Science Institute
School of Chemistry
The University of Manchester
Monday, February 6, 2012
EMSL Auditorium
11:00AM

Bose-Einstein Condensation (BEC) was first achieved in the liquid phase in helium a century and, for gas phase atoms, a decade ago. The question arises if there could be a third BEC of a solid, crystalline, state. A possible pathway towards such a new state of matter is a quantum plasma for which the de Broglie wavelength becomes larger than the mean distance between particles. For the electrons in an ultra-cold ion-electron plasma this condition is fulfilled for a temperature below 0.1K and a density above  1015 cm3.  We produce such an ultra-cold Rydberg plasma by laser threshold ionization of NO molecules in the high-density expansion region of a supersonic jet close to the nozzle. This plasma has an extremely long lifetime of milliseconds, and it shows the compressibility of a "sponge like" ultra-soft solid.  An explanation is the formation of an electron Wigner crystal, which according to A A Abrikosov should also lead to the formation of a lattice of the cations.  A possible cooling mechanism for the molecular cations (such as 14N16O+ Bosons) towards quantum degeneracy, i.e. a molecular Bose-Einstein Condensate, will be discussed.

2011

Douglas Doren
Douglas Doren

Douglas Doren

"Aqueous Solvation in Extreme Conditions: Accurate Calculations when Accurate Measurements are not Possible"

Professor, Chemistry and Biochemistry
Associate Dean, Arts and Sciences
University of Delaware
Tuesday, May 17, 2011
EMSL Auditorium
10:00AM

High temperature aqueous solutions are central to many natural and industrial processes but their properties can only be measured accurately over a limited range of temperature and density. I will describe a computational approach that allows simulations of thermodynamic properties of such systems from first principles. This approach is a QM/MM method that combines configurational averaging from molecular dynamics or Monte Carlo simulations with accurate quantum chemistry calculations of energies. The method was initially developed for understanding solvation in high temperature water, and it is especially efficient in such systems. Applications to supercritical water and solvation of sodium chloride at high temperatures will be described, followed by more recent work on low-temperature aqueous aerosols. Several comparisons to experiment as well as internal validation methods confirm the reliability of the approach. In conditions where accurate experimental measurements are not possible, this computational method provides a new source of reliable data.


George Schatz
George Schatz

George Schatz

"Plasmon-enhanced Optical Phenomena"

Editor-in-Chief, Journal of Chemical Physics
Morrison Professor of Chemistry, Northwestern University
Monday, March 14, 2011
EMSL Auditorium
11:00AM

Silver and gold nanoparticles have strong absorption and scattering in the visible and near-infrared as a result of plasmon excitation. The optical properties of these particles can be tuned by varying nanoparticle size (in the few nm to few hundred nm range) and shape, and generally these properties can be effectively modeled using classical electromagnetic theory. However, there are aspects of these optical properties where the classical picture fails, and then it is necessary to incorporate quantum effects into the theoretical description. This talk describes our latest work with understanding surface-enhanced Raman scattering from silver and gold nanoparticles and nanostructures, with emphasis on data from the Van Duyne and Mirkin groups concerned with dimer structures that have a small gap (~1 nm) between 100 nm particles. I will also describe the use of silver-coated nanoparticles for plasmon enhancement in dye-sensitized solar cells.


Einar Uggerud
Einar Uggerud

Einar Uggerud

"Structural Rearrangements and Proton Transfer within Water Clusters of Atmospheric Relevance"

Head of Mass Spectrometry Lab
University of Oslo
Friday, February 25, 2011
EMSL Auditorium
11:00AM

Hydrogen/deuterium exchange induced in reactions of various protonated or deprotonated water clusters, (X)(Y)(H2O)n (1 ≤ n≤ 30; containing ammonia, pyridine and/or hydrogen sulfate) with heavy water has been studied experimentally at near-thermal collision energies. The interpretation has been facilitated by quantum chemical calculations, including extensive Born-Oppenheimer molecular dynamics simulations. Lifetimes of the collision complexes have been estimated using RRKM theory. The experiments reveal unique and surprising details of the structure and dynamics of water clusters. For a given cluster size, both the total cross-section for isotope exchange and the relative amount of single and double substitution of H by D depends on the chemical properties of the core molecules X and Y. The experimental observations can be rationalized on the basis of the basicity and solubility of the core molecules X and Y. It appears that single H/D exchange is proton catalyzed, while double substitution has contributions from this mechanism as well as from ligand exchange. The tendency for a proton to migrate within a water cluster is determined by a fine balance between the relative proton affinities of the various basic sites. Solute molecules may slow down proton migration by having high proton affinity. On the other hand, water solvation and local hydrogen bond patterns may modify the proton affinity of a given site significantly.


Thom H. Dunning, Jr, Ph.D.
Thom H. Dunning Jr, Ph.D.

Thom H. Dunning, Jr, Ph.D.

"Main Group Chemistry Beyond First Row: The Remarkable Chemistry of the Late p-Block Elements"

Director, National Center for Supercomputing Applications;
Professor, Distinguished Chair for Research Excellence in Chemistry
Thursday, February 24, 2011
EMSL Auditorium
2:30PM

Chemists have employed computational modeling to understand the structures, spectra, energetics and reactivities of the first row elements (Li-F) with great success. But, it has long been recognized that the chemistry of the main group elements in the second and subsequent rows of the p-block of the Periodic Table differs dramatically from that of their first row counterparts. This "first row anomaly" is well recognized in inorganic chemistry, and many reasons have been advanced to explain the difference.

One of the most striking differences between the first and subsequent row elements is the ability of the latter row elements to "expand their valence shell," forming hypervalent molecules such as PCl5, SF4/SF6 and ClF3/ClF5. Recent studies of the fluorides of phosphorus, sulfur and chlorine revealed that (i) hypervalency was the result of a new type of bonding, recoupled pair bonding, that results when a pair of electrons in a lone pair orbital are recoupled to form a bond with a ligand using one of the electrons in the pair, (ii) recoupled pair bonding is common in non-hypervalent molecules, e.g., recoupled pair bonding leads to bound, low-lying excited 4S-, 2S- and 2D states in SF and the 3B1 and 3A2 excited states in SF2, and (iii) recoupled pair bonding has a dramatic effect on the structure, spectra and energetics of the XFn species The ability of electronegative ligands to recouple the electrons in the lone pair orbitals of second and higher row late p-block elements is a major factor in the anomalous behavior of these elements, including their unusual reactivities.

The seminar will introduce the basic features of recoupled pair bonding and illustrate how recoupled pair bonding affects the structure, spectra and bond energies of second row compounds.


Prof. Richard Haglund
Richard Haglund

Professor Richard Haglund

"Microscopic Views of a First-Order Phase Transition in a Strongly Correlated Transition Metal Oxide"

Research Highlight: Molecular Magician

Department of Physics and Astronomy
Vanderbilt University
Thursday, February 3, 2011
EMSL Auditorium
11:00AM

Vanadium dioxide, first synthesized in bulk crystalline form half a century ago, undergoes a first-order phase transition from a semiconductor to a metal at approximately 70°C that can be triggered electrically, optically or thermally. The mechanism of the phase transition appears to involve both electronic (metal-insulator) and structural (monoclinic-to-tetragonal) components, and the detailed dynamics of the transition depends crucially on the mode of excitation. Recent experiments with time (length) resolution down to tens of femtoseconds(nanometers) are opening up a truly microscopic understanding of the ways in which materials synthesis, sample morphology and dimensionality are interconnected with the kinetics and dynamics of the phase transformation. This understanding, in turn, is opening up interesting applications of vanadium dioxide in plasmonics, metamaterialsand silicon photonics.


Konrad Thurmer, Ph.D
Konrad Thürmer, Ph.D.

Konrad Thürmer, Ph.D.

"Deciphering the morphology of ice films on metal surfaces"

Research Highlight: Molecular-level Insights into the Formation of Ice

Material Physics Department
Sandia National Laboratories
Thursday, January 27, 2011
EMSL Auditorium
2:15PM

Although extensive research has been aimed at the structure of ice films, questions regarding basic processes that govern film evolution remain. Recently we discovered how ice films as many as 30 molecular layers thick can be imaged with STM. The observed morphology yields insights about water-solid interactions and how they affect the structure of ice films. This talk gives an overview of this progress for crystalline ice films on Pt(111). STM reveals a first molecular water layer very different from bulk ice: besides the usual hexagons, it also contains pentagons and heptagons. Slightly thicker films (~1 nm, at T>120K) are comprised of ~3-nm-high crystallites, surrounded by the one-molecule-thick wetting layer. These crystals dewet by nucleating layers on their top facets. Measurements of the nucleation rate as a function of crystal height provide estimates of the energy of the ice-Pt interface. For T>115K surface diffusion is fast enough that surface smoothing and 2D-island ripening is observable. By quantifying the T-dependent ripening of island arrays, we determined the activation energy for surface self-diffusion. The shape of these 2D islands varies strongly with film thickness. We attribute this to a transition from polarized ice at the substrate towards proton disorder at larger film thicknesses. Despite fast surface diffusion ice multilayers are often far from equilibrium. For example, ice grows between ~120 and ~160 K in its cubic variant rather than in its equilibrium hexagonal form. We found this to be a consequence of the mismatch in the atomic Pt-step height and the ice-bilayer separation and propose a mechanism of cubic-ice formation via growth spirals around screw dislocations.


2010

Will Castleman
Will Castleman

Professor Will Castleman

"Clusters, Catalysis, and Materials: Kinetic, Superatomand IsoelectronicConcepts"

Research Highlight: An Alchemist's Dream: Superatoms Mimic Elements

Department of Chemistry and Physics
Penn State University
Monday, May 10, 2010
EMSL Auditorium
11:00AM

During the course of investigating the reactivity and structure of metal and metal-compound clusters, we discovered the ability to mimic elements of the periodic table using selected species termed "superatoms". The findings are being extended to binary metallic and compound systems, where both electronic and geometric structures are identified as playing a role in governing stability and the presence of reactive centers, the main subject of this lecture. As the behavior of clusters can be controlled by size and composition, the superatoms offer the potential to create unique compounds with tailored properties where each atom makes a difference. Having demonstrated the feasibility of this approach, one of the prime objectives of our current research is to lay the foundation for forming new nanoscale materials via techniques of cluster assembly utilizing these "elements" as the building blocks, utilizing knowledge we acquire about cluster reactions and properties which serve to identify promising species. This pursuit is viewed as one of the most promising frontiers in nanoscale materials research.

It is found that clusters of selected composition, stoichiometry, size and charge-state provide ideal media for investigating fundamental mechanisms of heterogeneous catalysis, especially for oxidation reactions. The interplay and unification of the ideas and concepts that enable the identification of catalytic mechanisms and the design of superatoms mimicking elements of the periodic table will be discussed, also with attention given to quantifying concepts through the isoelectronic principle.


Murray Johnston
Murray Johnston

Professor Murray Johnston

"Adventures in Aerosol Mass Spectrometry: Field and Laboratory Investigations"

Department of Chemistry and Biochemistry
University of Deleware
Tuesday, February 16, 2010
EMSL Auditorium
10:00AM

Aerosol mass spectrometers measure the time-resolved chemical composition of airborne particles. Our laboratory has developed several instruments, each based on a different detection principle targeting a specific combination of particle size and chemical components—from the nanometer to micrometer size range and from semivolatile organic compounds to refractory inorganic materials. These instruments have been used in the field to characterize ambient air and in the laboratory to study chemical processes associated with particle formation and growth. This presentation will provide an overview of the methodology associated with these instruments and what they tell us about atmospheric processes.


2009

Miquel Salmeron
Miquel Salmeron

Professor Miquel Salmeron

"Molecular level studies of the growth of water on metals and oxides"

Director, Materials Sciences Division
Lawrence Berkeley National Laboratory
Thursday, December 3rd, 2009
EMSL/Auditorium
1:30PM

Wetting, reactivity, solvation and growth are important phenomena that govern our environment, the operation of electrochemical systems and catalysis. And yet, the structure of interfacial water is surprisingly still largely unknown. Important questions include the structure of the layer of water in contact with the surface, the occurrence of dissociative reactions, the role of O and H bonds with the surface and with other molecules, etc. Equally important is the structure of the 2nd, 3rd and subsequent water layers and how their structures differ from that of the first layer until becoming equal to bulk water. I will discuss old and new results obtained in my laboratory that provide some answers to these questions. We use microscopy and spectroscopy tools, including Scanning Probes (AFM, STM) and Spectroscopy, particularly the new Ambient Pressure Photoelectron spectroscopy, that operate both in vacuum and under ambient conditions. I will discuss results obtained on clean metals (Ru, Pd, Cu), metals covered with oxygen layers, and on surfaces of oxides, where cluster formation, dissociation and growth can be followed with molecular level resolution


Rigoberto Hernandez
Rigoberto Hernandez

Professor Rigoberto Hernandez

"Shake, rattle and rip: The far-from-equilibrium dynamics of colloids"

School of Chemistry & Biochemistry
Georgia Institute of Technology
Friday, November 20th, 2009
EMSL/Auditorium
1:30PM

Colloidal dispersions have been useful for many applications particularly because of the balance of microscopic heterogeneity and the wealth of tunable properties they exhibit at macroscopic length scales. One possible additional tunable parameter to control structure and function of colloidal formulations would arise from the effects of dynamic (or time-dependent) microscopic structure changes. We will discuss on-going theoretical and computational work which suggests that such nonequilibrium conditions can indeed give rise to novel molecular motion within colloidal suspensions. Specifically, suspensions of driven colloids—with a shape that changes in size or orientation—have been described using molecular dynamics simulations, coarse-grained particle dynamics simulations, and stochastic models. The nonequilibrium dynamics within these driven colloidal suspensions are not presently well understood because they involve several disparate time and length scales, but are increasingly being explored experimentally using optical microscopy of various nanoparticle suspensions. Examples of such materials include core-shell hydrogels and lyotropic liquids with magnetically alignable mesogens.

We have shown that in some cases the motion (such diffusion or molecular reorganization) arises as the projection of a simple model of a chemical system bilinearly coupled to a harmonic bath with a time-dependent coupling. Moreover, the stochastic model can be used to surmise the diffusion of a tagged particle in a colloidal suspension which swells or shrinks with time. The nonequilibrium stochastic model has also allowed us to define an equilibrium temperature for a particle coupled to multiple time-dependent unequal-temperature baths. It has been verified using a particle-based model. The structure of these materials also plays an important role in the correlations of the dynamics of the probe even when the structure is static as in the so-called Lorentz models. Recent results of the dynamics both within static sheared fluids will also be presented.


Stephen Leone
Stephen Leone

Dr. Stephen Leone

"X-Ray Probing of Atomic and Molecular Dynamics in the Attosecond Limit"

University of California, Berkeley
Lawrence Berkeley National Laboratory
Monday, November 9, 2009
EMSL/Auditorium
2:00PM

Pulses of soft x-rays produced by high harmonic generation of intense laser pulses are used to probe atomic and molecular processes through core level spectroscopy, revealing ionization, alignment, bond breaking, and intramolecular dynamics. The high harmonic process is also a key to create isolated attosecond pulses to study the timescales of electronic dynamics. With a new method of ultrafast transient absorption, the high harmonics are spectrally resolved after the sample to reveal the spectral transitions at various short delay times, into the attosecond limit. The methods are applied to alignment dynamics in high field ionization, molecular dissociative ionization, and wave packet dynamics among vibrational and electronic states.


Todd Martinez
Todd Martinez

Dr. Todd Martinez
Friday, October 30, 2009
EMSL/Auditorium
2:30PM

"Photochemistry and Mechanochemistry from First Principles Dynamics"



Dr. Rich Saykally
Dr. Rich Saykally

Dr. Rich Saykally

"Select Adsorption of Ions to Aqueous Interfaces"

College of Chemistry
University of California, Berkeley
Wednesday, May 13, 2009
EMSL/Auditorium
10:00AM



Dr. David Chandler
Combustion Research Facility, Sandia National Laboratories, Livermore

"The Quest for Ultracold Molecules"

Dr. David Chandler
Dr. David Chandler

Friday, March 20, 2009
EMSL Auditorium
11:00AM
The cooling of atoms to ultracold temperatures, where the quantum nature of the gas dominate their interactions, has resulted in spectacular discoveries, such as the realization and study of new states of matter like Bose Einstein Condensates, degenerate Fermi gasses, and Bardeen, Cooper Schrieffer fluids. In addition to forming new states of matter, cooling atoms to microKelvin temperatures, and below, has enabled ultra-high resolution spectroscopy studies and the extraction of information about the collisional dynamics of atoms and their interactions.

All of these areas of research have molecular analogs. The added complexity found in molecules offers the possibility of rich areas of investigation in spectroscopy, collision dynamics, etc. However, the field of ultracold molecule studies had remained generally unexplored due to the complexity of making ultracold samples.

In this seminar, Dr. Chandler will discuss the state of the field for making samples of ultracold molecules and show the recent progress in the technique of Kinematic Cooling. This technique uses a single collision with an appropriate atom to remove the translational motion from a molecule, thereby cooling it. Connection to other areas of physical chemistry, such as the near threshold photodissociation of van der Waals molecules, will also be discussed.



An interview with Dr. Carl Lineberger, University of Colorado, speaks to the role of chemical physics in society. Dr. Lineberger asserts that chemical physics was the discipline that first provided a molecular basis for all kinds of physical properties. He also promotes the use of interdisciplinary teams to solve complex problems.

W. Carl Lineberger
Prof. Dr. W. Carl Lineberger University of Colorado

"Time resolved photoelectron spectroscopy of partially solvated anions"

Friday, January 9, 2009
EMSL Auditorium
1:00PM
Ultrafast pump-probe studies of recombination in partially solvated, size-selected dihalide cluster anions show long time coherent motions and the resulting non-statistical energy flow in the cluster. For photodissociated I2 -(CO2)n, we observe a new type of recombination: a solvent asymmetry-driven energy transfer process without a condensed phase counterpart. Very short recombination times are observed (~10 ps) with the chromophore only partially solvated, and the recombination time steadily decreases with additional solvation. Theoretical models point to the central role of the solvent electric field in the recombination process, but suggest electron transfer processes that cannot be tested with a homonuclear dihalide chromophore. To further test these concepts, we investigate the time-resolved recombination of photodissociated IBr -(CO2)n clusters following excitation to the dissociative IBr -2II1/2 state of the chromophore. In complete contrast to previous studies involving solvated I2 -, the observed recombination times for IBr -(CO2)n increase dramatically with increasing cluster size. The basis for this dramatic difference gives increased credence to the utility of a "solvent coordinate" description of geminate recombination. Preliminary experiments utilizing time-resolved photoelectron spectroscopy of the photodissociated anion show directly the solvent-driven electron transfer, and permit the development of dynamical models that show the role of the solvent in assisting long-range electron transfer.

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