Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session C31: Journal of Chemical Physics Editor's ChoiceInvited
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Sponsoring Units: DCP Chair: David Nesbitt, JILA, University of Colorado Room: 331 |
Monday, March 14, 2016 2:30PM - 3:06PM |
C31.00001: JCP Editors Choice Award - Theoretical Methods and Algorithms Invited Speaker: Todd Gingrich . [Preview Abstract] |
Monday, March 14, 2016 3:06PM - 3:42PM |
C31.00002: Elucidation of Chemical Reactions by Two-Dimensional Resonance Raman Spectroscopy Invited Speaker: Andrew Moran Two-dimensional (2D) Raman spectroscopies were proposed by Mukamel and Loring in1985 as a method for resolving line broadening mechanisms of vibrational motions in liquids. Significant technical issues challenged the development of both five- and seven-pulse 2D Raman spectroscopies. For this reason, 2D Raman experiments were largely abandoned in 2002 following the first demonstrations of 2D infrared spectroscopies (i.e., an alternate approach for obtaining similar information). We have recently shown that 2D Raman experiments conducted under electronically resonant conditions are much less susceptible to the problems encountered in the earlier 2D Raman work, which was carried out off-resonance. In effect, Franck-Condon activity obviates the problematic selection rules encountered under electronically off-resonant conditions. In this presentation, I will discuss applications of 2D resonance Raman spectroscopies to photodissocation reactions of triiodide and myoglobin. It will be shown that vibrational resonances of the reactants and products can be displayed in separate dimensions of a 2D resonance Raman spectrum when the photo-dissociation reaction is fast compared to the vibrational period. Such 2D spectra expose correlations between the nonequilibrium geometry of the reactant and the distribution of vibrational quanta in the product, thereby yielding insight in the photo-dissociation mechanism. Our results suggest that the ability of 2D resonance Raman spectroscopy to detect correlations between reactants and products will generalize to other ultrafast processes such as electron transfer and energy transfer. [Preview Abstract] |
Monday, March 14, 2016 3:42PM - 4:18PM |
C31.00003: Photoexcited Nuclear Dynamics with Ab Initio Electronic Structure Theory: Is TD-DFT Ready For the Challenge? Invited Speaker: Joseph Subotnik In this talk, I will give a broad overview of our work in nonadiabatic dynamics, i.e. the dynamics of strongly coupled nuclear-electronic motion whereby the relaxation of a photo-excited electron leads to the heating up of phonons. I will briefly discuss how to model such nuclear motion beyond mean field theory. Armed with the proper framework, I will then focus on how to calculate one flavor of electron-phonon couplings, known as derivative couplings in the chemical literature. Derivative couplings are the matrix elements that couple adiabatic electronic states within the Born-Oppenheimer treatment, and I will show that these matrix elements show spurious poles using formal (frequency-independent) time-dependent density functional theory. To correct this TD-DFT failure, a simple approximation will be proposed and evaluated. Finally, time permitting, I will show some ab initio calculations whereby one can use TD-DFT derivative couplings to study electronic relaxation through a conical intersection. [Preview Abstract] |
Monday, March 14, 2016 4:18PM - 4:54PM |
C31.00004: Simulations of mean ionic activity coefficients and solubilities in aqueous electrolyte solutions Invited Speaker: Athanassios Panagiotopoulos Aqueous electrolyte solutions play an important role in industrial, geochemical and biological applications. The mean ionic activity coefficients quantify the deviation of salt chemical potential from ideal solution behavior; experimental measurements are available for many salts over broad ranges of concentration and temperature, but there have been practically no prior simulation results, because if sampling difficulties for explicit-solvent electrolyte solutions. We have developed a new approach for determination of activity coefficients of aqueous electrolytes [1]. Common fixed-point-charge models for water and ions are unable to reproduce simultaneously activity coefficients and solubilities. Polarizable models perform better, but still predict an incorrect temperature dependence of these properties [2]. [1] Z. Mester and A. Z. Panagiotopoulos ``Mean ionic activity coefficients in aqueous NaCl solutions from molecular dynamics simulations," \textit{J. Chem. Phys.} \textbf{142}: 044507, 10 pp (2015). \underline {http://dx.doi.org/10.1063/1.4906320} [2] H. Jiang, Z. Mester, O. A. Moultos, I. G. Economou, and A. Z. Panagiotopoulos, "Thermodynamic and Transport Properties of H2O$+$NaCl from Polarizable Force Fields," J\textit{. Chem. Theory Comput}. \textbf{11}: 3802-3810 (2015). \underline {http://pubs.acs.org/doi/abs/10.1021/acs.jctc.5b00421} [Preview Abstract] |
Monday, March 14, 2016 4:54PM - 5:30PM |
C31.00005: Chirality-sensitive microwave spectroscopy - application to terpene molecules Invited Speaker: Melanie Schnell Most molecules of biochemical relevance are chiral. Even though the physical properties of two enantiomers are nearly identical, they might exhibit completely different biochemical effects, such as different odor in the case of carvone. In nature and as products of chemical syntheses, chiral molecules often exist in mixtures with other chiral molecules. The analysis of these complex mixtures to identify the molecular components, to determine which enantiomers are present, and to measure the enantiomeric excesses (ee) is still one of the challenging and very important tasks of analytical chemistry. We recently experimentally demonstrated a new method of differentiating enantiomeric pairs of chiral molecules in the gas phase. It is based on broadband rotational spectroscopy and is a three-wave mixing process that involves a closed cycle of three rotational transitions. The phase of the acquired signal bares the signature of the enantiomer, as it depends upon the product of the transition dipole moments. Furthermore, because the signal amplitude is proportional to the ee, this technique allows not only for determining which enantiomer is in excess, but also by how much. A unique advantage of our technique is that it can also be applied to mixtures of chiral molecules, even when the molecules are very similar. In my lecture, I will introduce the technique and give an update on the recent developments. [Preview Abstract] |
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