Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session M27: Invited Session: Prize Session: Broida, Pyler, Langmuir, Phd |
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Sponsoring Units: DCP Chair: David Chandler, Sandia National Laboratories Room: 204B |
Wednesday, March 4, 2015 11:15AM - 11:27AM |
M27.00001: Introduction David Chandler |
Wednesday, March 4, 2015 11:27AM - 12:03PM |
M27.00002: Herbert P. Broida Prize Talk: Molecular photofragmentation dynamics in the gas and condensed phase: similarities and differences Invited Speaker: Michael Ashfold Phenols and azoles are important chromophores in the nucleobases and aromatic amino-acids that dominate the near-UV absorption spectra of many biological molecules. $\pi $*$\leftarrow \pi $ excitations are responsible for these strong UV absorptions, but these molecules also possess excited states formed from $\sigma $*$\leftarrow \pi $ electron promotions. $\pi \sigma $* excited states typically have much smaller absorption cross-sections, but their photochemical importance is becoming ever more widely recognized [1]. We have used photofragment translational spectroscopy (PTS) methods (and complementary \textit{ab initio} theory) to explore X--H bond fission (X $=$ heteroatom) following UV photoexcitation of many such heteroaromatic molecules in the gas phase and, more recently, started ultrafast pump-probe studies of the same (and related) processes in solution. This presentation will (i) summarize the state of knowledge derived from PTS studies of phenol and related molecules in the gas phase [2], (ii) highlight the extent to which such knowledge can inform our interpretation of ultrafast pump-probe studies of the UV photofragmentation of similar molecules ((thio)phenols, anisoles and ethers) in solution [3,4] and (iii) demonstrate how such solution phase studies offer a route to exploring photoinduced ($\pi \sigma $*-state mediated) ring opening of heterocyclic molecules like furans and thiophenes [5]. \\[4pt] [1] See, $e.g$., M.N.R. Ashfold, G.A. King, D. Murdock, M.G.D. Nix, T.A.A. Oliver and A.G. Sage, \textit{Phys. Chem. Chem. Phys}. \textbf{12}, (2010), 1218. \\[0pt] [2] T.N.V. Karsili, A.M. Wenge, S.J. Harris, D. Murdock, J.N. Harvey, R.N. Dixon and M.N.R. Ashfold, \textit{Chem. Sci}. \textbf{4}, (2013), 2434.\\[0pt] [3] Y. Zhang, T.A.A. Oliver, M.N.R. Ashfold and S.E. Bradforth, \textit{Farad. Disc. Chem. Soc.} \textbf{157}, (2012), 141.\\[0pt] [4] S.J. Harris, D. Murdock, Y. Zhang, T.A.A. Oliver, M.P. Grubb, A.J. Orr-Ewing, G.M. Greetham, I.P. Clark, M. Towrie, S.E. Bradforth and M.N.R. Ashfold, \textit{Phys. Chem. Chem. Phys}. \textbf{15}, (2013), 6567. \\[0pt] [5] D. Murdock, S.J. Harris, J. Luke, M.P. Grubb, A.J. Orr-Ewing and M.N.R. Ashfold, \textit{Phys. Chem. Chem. Phys}. \textbf{16}, (2014), 21271. [Preview Abstract] |
Wednesday, March 4, 2015 12:03PM - 12:39PM |
M27.00003: Earle K. Plyler Award: X-Ray and UV Studies of Molecular and Nano-Systems at the Atomic-Scale Resolutions of Time and Space Invited Speaker: Majed Chergui The advent of femtosecond (fs) laser technology some twenty five years ago opened a whole new era in Science because of its ability to probe in ``real-time'' nuclear motion in molecules, crystals, liquids and proteins. In the past fifteen years, huge efforts have been deployed aimed at combing the high time resolution of fs lasers with the high spatial resolutions of structural techniques, such as X-ray spectroscopies. In addition, lab-based sources of ultrashort vacuum ultraviolet and soft X-rays based on the process of High Harmonic Generation have made it possible to study the underlying electronic structure changes which drive the actual structural dynamics of systems. In the optical domain, huge efforts have been deployed in extending the availability of sources to the UV below 300 nm, which is very important for the study of small molecules, amino-acid residues, nucleotides or metal oxides as they all absorb in this region. We will present some of our recent studies using ultrafast X-ray absorption spectroscopy and 2-dimensional UV spectroscopy for the study of molecular systems and nanoparticles. I will also discuss the perspectives these methods offer for materials science, chemistry and biology. [Preview Abstract] |
Wednesday, March 4, 2015 12:39PM - 1:15PM |
M27.00004: Irving Langmuir Prize Lecture - A predictive theory of transition metal surface catalysis Invited Speaker: Jens Norskov The lecture will outline a theory of heterogeneous catalysis that allows a detailed understanding of elementary chemical processes at transition metal surfaces and singles out the most important parameters determining catalytic activity and selectivity. It will be shown how scaling relations allow the identification of descriptors of catalytic activity and how they can be used to construct activity and selectivity maps. The maps can be used to define catalyst design rules and examples of their use will be given. [Preview Abstract] |
Wednesday, March 4, 2015 1:15PM - 1:51PM |
M27.00005: Electron Transport, Energy Transfer, and Optical Response in Single Molecule Junctions Invited Speaker: Alexander White The field of molecular electronics has grown significantly since the first measurements of single molecule conductance. The single molecule junction, a device in which two conducting leads are spanned by a single molecule, has become a powerful tool for studying charge transfer at the molecular level. While early experiments were focused on elastic electron conductance, today measurements of vibronic effects, molecular optical response, spintronics, thermal conductance, and quantum interference and decoherence effects are prominent areas of research. These new experimental advancements demand improved theoretical treatments which properly account for the interactions between different degrees of freedom: charge, electronic, vibrational, spin, etc.; all in physically relevant parameter ranges. This talk focuses on using a many-body states based approach to investigate the regime of strong interaction between these degrees of freedom, with relatively weak coupling between the molecule and the electric reservoirs created by the conducting leads. We focused on three related processes, electron transfer, electronic energy transfer and molecular excitation.\\[4pt] In collaboraton with Boris Fainberg, Faculty of Sciences, Holon Institute of Technology; Sergei Tretiak, Theoretical Division, Center for Integrated Nanotechnologies, Los Alamos National Laboratory; and Michael Galperin, Department of Chemistry and Biochemistry, University of California San Diego. [Preview Abstract] |
Wednesday, March 4, 2015 1:51PM - 2:03PM |
M27.00006: First Steps in Atmospheric Particle Formation: Nucleation of the Smallest Ice Snowflake Jozef Lengyel, Juraj Fedor, Jaroslav Kocisek, Viktoriya Poterya, Andriy Pysanenko, Michal Farnik The study of atmospheric aerosols attracts a considerable attention because of its influence on atmospheric chemistry and climate. Perhaps the most famous example is the ozone hole where the polar stratospheric clouds play a key role in the ozone depletion process. The atmospheric cloud generation starts with the growing of small ice nanoparticles via uptake of molecules on water clusters. Therefore the cross-sections for uptake have been investigated. The measured cross sections of ice particles can be more than twice larger than the geometrical cross sections of these particles.\footnote{J. Lengyel et al. \textbf{J Chem Phys} 137, 2012, 034304} This can have significant consequences in modelling of growth ice nanoparticles. Subsequently, we have investigated the size-dependence of the measured cross-sections for water clusters. Here, the cross sections of water clusters depart from the theoretically predicted dependence and are considerably larger starting from the clusters of approximately 300 water molecules. We interpret this increase of cross section by the occurrence of highly irregular water cluster shapes, e.g. formation of the ``nanosnowflakes''.\footnote{J. Lengyel et al. \textbf{Phys Rev Lett} 112, 2014, 113401} [Preview Abstract] |
Wednesday, March 4, 2015 2:03PM - 2:15PM |
M27.00007: Probing Individual Atoms and Molecules on Pt(111) Zhu Liang A low-temperature scanning tunneling microscopy (LT-STM) is used to investigate the structure and reactivity of atomic nitrogen on Pt surfaces, which is important to a variety of catalytic processes. The adsorption of ammonia on an oxygen covered Pt surface leads to the formation of an NH$_{3}$--O$_{2}$ complex. Such a complex serves as a precursor to ammonia oxydehydrogenation, which produces an ordered atomic N layer on the surface when annealed to temperatures above 300 K. ($\sqrt{3} \times \sqrt{3}$)R30$^{\circ}$-N and p(2 $\times$ 2)-N phases are found to coexist at temperatures between 360 and 400 K. After exposing the N-covered surface to hydrogen gas at 300 K, NH molecules are present as scattered molecules, as well as in dense islands. Mechanisms of dissociation of NH and lateral movement of H have been explored by examining the threshold energies and reaction rates. Measuring the response of the motion against applied bias voltage reveals the threshold energy, which is the energy of the vibrational mode that is responsible for activating a given motion. A theoretical model is used to fit the spectra, from which an estimate of reaction rate is obtained. ND dissociation and D hopping have also been investigated to examine the role of tunneling in these reactions. [Preview Abstract] |
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