Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session D38: Earle K. Plyler Prize Session II: Spectroscopy |
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Sponsoring Units: DCP Chair: Sunney Xie, Harvard University Room: A130/131 |
Monday, March 21, 2011 2:30PM - 3:06PM |
D38.00001: Ultrafast Nonlinear Optical Spectroscopy or where would we be without Shaul Mukamel? Invited Speaker: The development of ultrafast nonlinear optical spectroscopy owes much to the pioneering work of Shaul Mukamel in developing a unifying framework and language with which to understand and relate the content of different types of experiment. The culmination of this work, to date, is in the development of multidimensional optical spectroscopies. In this talk, I will describe recent work in my group on two dimensional electronic spectroscopy of photosynthetic light-harvesting complexes and, if time permits, single walled carbon nanotubes and molecular systems relaxing via conical intersections. [Preview Abstract] |
Monday, March 21, 2011 3:06PM - 3:18PM |
D38.00002: 2D IR Spectroscopy of Protein Conformation, Folding, and Binding Kevin Jones, Andrei Tokmakoff, Ziad Ganim, Joshua Lessing, C. Sam Peng 2D IR spectroscopy is an increasingly powerful tool for investigation of protein structure and dynamics. As an ultrafast spectroscopy, it provides information on protein structure and conformational variation with high time resolution, providing a tool to study the dynamics of folding and binding. Some of the unique characteristics of 2D IR result from the powerful structure based modeling that is available for amide vibrations. This talk will cover recent examples from our group in which different forms of protein 2D IR and computational spectroscopy are used to reveal conformational heterogeneity in peptides, the folding and binding of proteins, and protein-water interactions. When combined with temperature-jump experiments, the formation and interchange of these structures is probed. [Preview Abstract] |
Monday, March 21, 2011 3:18PM - 3:30PM |
D38.00003: Three-dimensional Fourier-transform spectroscopy of potassium vapor Hebin Li, Alan Bristow, Mark Siemens, Galan Moody, Steven Cundiff We have implemented three-dimensional (3D) Fourier-transform spectroscopy to study potassium vapor contained in a $\sim$20 $\mu$m transmission cell with argon buffer gas. The four-wave mixing signal is measured in three time dimensions corresponding to the delays between three $\sim$100 fs, phase-stabilized excitation pulses that are arranged in the box geometry. The emission is detected using a phase-stabilized reference pulse by spectral interferometry, and other time axes are Fourier transformed to construct the 3D spectra. The 3D spectra contain the full information of third-order coherent response of the vapor, yet the contribution from each of the single-quantum excitation pathways is unambiguously isolated. Projecting a 3D spectrum onto a specific two-dimensional (2D) plane retrieves rephasing, non-rephasing, and T-scan 2D spectra, as well as the spectra that are not accessible by conventional 2D scans. The spectral features which overlap in congested 2D spectra can be isolated for studying unique processes represented by a single pathway. [Preview Abstract] |
Monday, March 21, 2011 3:30PM - 3:42PM |
D38.00004: Reflection Geometry Electronic Two-dimensional Fourier Transform Spectroscopy Thomas W. Jarvis, Zheng Sun, Xiaoqin Li, Mikhail Erementchouk, Michael N. Leuenberger Studying dynamics in nanostructures is vital to develop new opto-electronic devices and to understand fundamental processes in the solid state. Electronic Two-dimensional Fourier Transform Spectroscopy (2DFTS) is a powerful technique that coherently probes the nonlinear optical polarization, establishing correlations between absorption and subsequent emission or dispersion. We perform 2DFTS in reflection, a novel experimental geometry that allows us to probe structured materials. The coupling features and dimensionally extended lineshapes revealed by 2DFTS provide a description of decoherence and dephasing processes, coherent and incoherent energy transfer, and relaxation. [Preview Abstract] |
Monday, March 21, 2011 3:42PM - 4:18PM |
D38.00005: Ultrafast two dimensional infrared chemical exchange spectroscopy Invited Speaker: The method of ultrafast two dimensional infrared (2D IR) vibrational echo spectroscopy is described. Three ultrashort IR pulses tuned to the frequencies of the vibrational transitions of interest are directed into the sample. The interaction of these pulses with the molecular vibrational oscillators produces a polarization that gives rise to a fourth pulse, the vibrational echo. The vibrational echo pulse is combined with another pulse, the local oscillator, for heterodyne detection of the signal. For fixed time between the second and third pulses, the waiting time, the first pulse is scanned. Two Fourier transforms of the data yield a 2D IR spectrum. The waiting time is increased, and another spectrum is obtained. The change in the 2D IR spectra with increased waiting time provides information on the time evolution of the structure of the molecular system under observation. In a 2D IR chemical exchange experiment, two species A and B, are undergoing chemical exchange. A's are turning into B's, and B's are turning into A's, but the overall concentrations of the species are not changing. The kinetics of the chemical exchange on the ground electronic state under thermal equilibrium conditions can be obtained 2D IR spectroscopy. A vibration that has a different frequency for the two species is monitored. At very short time, there will be two peaks on the diagonal of the 2D IR spectrum, one for A and one for B. As the waiting time is increased, chemical exchange causes off-diagonal peaks to grow in. The time dependence of the growth of these off-diagonal peaks gives the chemical exchange rate. The method is applied to organic solute-solvent complex formation, orientational isomerization about a carbon-carbon single bond, migration of a hydrogen bond from one position on a molecule to another, protein structural substate interconversion, and water hydrogen bond switching between ions and water molecules. [Preview Abstract] |
Monday, March 21, 2011 4:18PM - 4:30PM |
D38.00006: Can the Isomerization of Retinal in Bacteriorhodopsin be Coherently Controlled in Strong Fields? Valentyn Prokhorenko, Alexei Halpin, Philip Johnson, Leonid Brown, Dwayne Miller Conflicting results have been obtained between weak field experiments (one-photon absorption) [1] and strong field recent studies [2] (multi-photon effects). Here we present our strong field experiments performed using linearly-chirped excitation pulses. Contrary to [2], we clearly observe phase-dependent control of photoproduct yield over a wide range of excitation energies. Above the excitation limit of $\sim $200 GW/cm$^{2}$ our results do however come into agreement with [2], but only for a single observation wavelength (650 nm) whereas the transient spectra unambiguously show drastic changes in the protein due to its ionization. At these excitation levels, this deleterious side channel precludes correct determination of the amount of 13-cis isomer. As such, we argue that it is impossible to make assignments of mechanistic details of control at a high field that in effect ``kills'' the protein. [1] V. I. Prokhorenko, A. M. Nagy, S. A. Waschuk, L. S. Brown, R. R. Birge, and R. J. D. Miller, Science 313, 1257- 1261 (2006). [2] A. C. Florean et al., PNAS 106, 10896-10900 (2009). [Preview Abstract] |
Monday, March 21, 2011 4:30PM - 4:42PM |
D38.00007: Toward Investigating Protein Folding Using the Combination of Computer Simulation and Spectroscopy Wei Zhuang Protein folding is an important problem that is attracting scientists from a wide range of disciplines. One of the major challenges comes from the gap between the experimental and the theoretical studies. We proposed a computational protocol of simulating the T-jump peptide unfolding experiments and the related transient IR and 2DIR spectra based on the Markov State Model (MSM) and Nonlinear Exciton Propagation (NEP) methods. MSMs partition the conformation space into a set of non-overlapping metastable states, and we can calculate spectra signal for each of these states using NEP method. Thus the overall spectroscopic observable for a given system is simply the sum of spectra of different metastable states weighted by their populations. Simulated spectra based on MSM have a much better agreement with the equilibrium experimental 2DIR spectra compared to MD simulations starting from the folded state. MSMs are also capable of simulating the unfolding relaxation dynamics upon the temperature jump. The agreement of the simulation using MSMs and NEP with the experiment provides a justification for our protocol as well as a physical insight underlying the spectroscopic observables. [Preview Abstract] |
Monday, March 21, 2011 4:42PM - 4:54PM |
D38.00008: Supersymmetry and fluctuation relations for currents in closed networks Vladimir Chernyak, Nikolai Sinitsyn The discovery of fluctuation theorems and nonequilibrium work relations has stimulated considerable interest in nonequilibrium statistical mechanics and theory of counting statistics. It is important to obtain exact relations that do not directly rely on the thermodynamic concepts, such as work or entropy, but rather describe unambiguous microscopic characteristics, such as statistics of particle currents in systems driven by time-dependent fields. We identify hidden supersymmetry in evolution, governed by the master equation, that survives on the level of the counting statistics of stochastic particle currents. Supersymmetry connects the evolutions in the spaces of populations (boson component) and empirical currents (fermion component). We present exact relations for statistics of currents in strongly driven mesoscopic stochastic systems. Being reminiscent of known fluctuation theorems, a part of our exact result is not directly related to the condition of microscopic reversibility but rather follows from {\it supersymmetry} of the counting statistics of currents. [Preview Abstract] |
Monday, March 21, 2011 4:54PM - 5:06PM |
D38.00009: Understanding Metal-Adsorbate Binding with Surface-Enhanced Raman Spectroscopy: Theory and Experiment Alexey Zayak, Hyuck Choo, Ying Hu, Jeffrey Bokor, Stefano Cabrini, James Schuck, Jeffrey Neaton Building on recent work [1], we use a combination of density functional theory (DFT) calculations and surface-enhanced Raman spectroscopy (SERS) measurements to explain experimentally observed variations in SERS data of an organic molecule, trans-1,2-two (4-pyridyl) ethylene (BPE). For the BPE on Au surfaces, our DFT calculations provide a quantitative description of chemical enhancement (CE), and elucidate that variations reported in experiments arise from a convolution of two factors: a nonuniform frequency dependent electromagnetic enhancement, and dependence of CE on the sample incubation time. The later reveals aspects of the binding kinetics of BPE to Au surfaces.\\[4pt] [1] A. T. Zayak,et. al., arXiv:1011.1873v1 [Preview Abstract] |
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