Bulletin of the American Physical Society
2017 Annual Meeting of the APS Mid-Atlantic Section
Volume 62, Number 19
Friday–Sunday, November 3–5, 2017; Newark, New Jersey
Session J4: Chemistry, Spectroscopy, and Dynamics |
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Chair: Alexei Khalizov, New Jersey Institute of Technology Room: 225, Campus Center, NJIT |
Saturday, November 4, 2017 4:15PM - 4:51PM |
J4.00001: Dynamic Structural Disorder in Supported Metal Nanoparticles: A Blessing or a Curse? Invited Speaker: Anatoly Frenkel Negative thermal expansion and anomalous bond length disorder are but a few examples of non-bulk behaviors in supported metal nanoparticles. I will illustrate them using a prototypical catalytic system, a platinum particle in equilibrium with oxide support and adsorbate gas, as an example. By combining X-ray absorption and emission spectroscopies with DFT/MD simulations, I will show that many ``anomalies'' have their explanation in the heterogeneous structure, fluctuating over broad time-scale. By tracking the flow of charge to and from the nanoparticle in operando conditions, several competing interactions can be disentangled: metal-support, metal-adsorbate, and support- adsorbate. In the ongoing research at Brookhaven our team is tackling also another type of heterogeneity, the inter-particle one, by creating a modern toolbox for operando investigations by a combination of spectroscopy and imaging methods. These results are of interest to energy sciences: by learning how to sort out and navigate these complex structures and employ dynamics to tune up reactivity, one can learn how to rationally design a catalyst with the desired activity and selectivity. [Preview Abstract] |
Saturday, November 4, 2017 4:51PM - 5:03PM |
J4.00002: UV Photodissociation of SO$_{2}$ Before Oxygenation of the Early Earth Atmosphere Paul B. Diss, Andrew J. Pommersheim, Amy S. Mullin The photodissociation dynamics from vibronically excited SO$_{2}$ molecules is investigated using tunable, pulsed UV light (210-220 nm) and state-resolved high-resolution transient IR absorption spectroscopy. Dissociation is initiated with the tunable UV light and the photofragments are probed with 4.4 $\mu$m (2230-2300 cm$^{-1}$) light. Individual Doppler-broadened ro-vibrational states were measured to get nascent translational energy distributions, rotational energy, and branching ratios of the SO photofragments. Measurements near the UV photodissociation threshold shed light onto the quantum yield of the photofragments from the excited SO$_{2}$ molecule. UV-wavelength-dependent studies of product energy partitioning are done to investigate and characterize the dissociation dynamics of predissociative states resulting from non-adiabatic coupling. The results of this research give insight to unusual sulfur isotope effects seen in the early earth rock record attributed to UV photochemistry of SO$_{2}$. [Preview Abstract] |
Saturday, November 4, 2017 5:03PM - 5:15PM |
J4.00003: Using an Optical Centrifuge to Study CO$_{2}$ Super Rotor Collisions with He and Ar Buffer Gases Matthew J. Murray, Hannah M. Ogden, Millard H. Alexander, Amy S. Mullin Collisions of CO$_{2}$ super rotors with Ar and He buffer gases are investigated using state-resolved high resolution transient IR absorption spectroscopy. The CO$_{2}$ super rotors are generated with an optical centrifuge that captures and accelerates the molecules to extreme rotational states with oriented angular momentum. Polarization-sensitive Doppler-broadened line profiles characterize the anisotropic kinetic energy release and show that the CO$_{2}$ super rotors behave like molecular gyroscopes. Quenching of CO$_{2}$ rotational energy is more efficient with He collisions than with Ar collisions. The experimental results are compared with quantum scattering calculations performed on the He-CO$_{2}$ and Ar-CO$_{2}$ collision systems, providing insight into the J-specific collision cross sections and rates that control the relaxation. These studies reveal how mass, velocity, and rotational adiabaticity impact angular momentum relaxation and reorientation. [Preview Abstract] |
Saturday, November 4, 2017 5:15PM - 5:27PM |
J4.00004: Investigating Energy Transfer Dynamics of High J N$_{2}$O Super Rotors Tara J. Michael, Hannah M. Ogden, Matthew J. Murray, Amy S. Mullin State resolved collision dynamics of N$_{2}$O in high J states up to J = 205 were investigated by preparing super rotor molecules using an optical centrifuge. High resolution transient IR spectroscopy was used to measure Doppler-broadened transient line profiles for the J = 160, 180, and 195 rotational states at 5 Torr with signals at 50 ns corresponding to 2-3 gas kinetic collisions. The results show that the J = 160, 180, and 195 states have initial translational energies near 500 K, indicating that modest amounts of translational energy results from the first 3-5 gas kinetic collisions. Translational energy increases are seen as the collision number increases, showing that non-resonant energy transfer becomes important later in the collisional cascade. The translational temperatures for higher J states remain constant for longer periods of time, showing that thermal collisions of high J rotors are more adiabatic and have more near-resonant energy transfer. [Preview Abstract] |
Saturday, November 4, 2017 5:27PM - 5:39PM |
J4.00005: Spinning Molecules to Well-Defined J-States Hannah M. Ogden, Tara J. Michael, Matthew J. Murray, Amy S. Mullin The optical centrifuge is a laser based technique to trap and spin molecules to high J states. The rotational energy of the centrifuged molecules depends on the spectral bandwidth of the centrifuge laser and the molecules’ moment of inertia. This study investigates how controlling the spectral bandwidth of the centrifuge laser affects the initial distribution of centrifuged molecules. High resolution transient IR absorption spectroscopy is used to interrogate the initial distributions of N$_{2}$O, CO$_{2}$, and CO super rotor molecules. States populated directly in the centrifuge are expected to show prompt appearance relative to collision induced populations. Furthermore, line profiles of nascent centrifuged molecules will not have collision induced Doppler broadening. Line center transient absorption signals yield information about the time dependent appearance of initially populated J states. These studies provide information about the capture and acceleration efficiency of the optical centrifuge. [Preview Abstract] |
Saturday, November 4, 2017 5:39PM - 6:15PM |
J4.00006: Radioisotopes And Nuclear Isomers: Reaching Beyond Chemical Energy Storage For Energy And Power Applications Invited Speaker: James Carroll Energy storage in chemicals, whether fuels or batteries, forms the basis for the Army's many energy and power applications. However, these materials are limited in both energy density ($\sim10^{4}$ J/g) and practical longevity (a few years for batteries). There is considerable interest in moving beyond these limitations -– at the extreme, fissionable materials reach about 10$^{11}$ J/g intrinsic energy density, but nuclear reactors are not attractive for portable energy storage. For this reason, research has focused on radioisotopes and nuclear isomers (metastable excited nuclear states) as a means of pushing beyond the ``chemical barrier'' to reach greater energy densities and longer energy storage times. This presentation will survey basic research conducted by the Army Research Laboratory and collaborating institutions in national laboratories and academia aimed at determining the feasibility of radioisotopes and nuclear isomers for energy and power applications. [Preview Abstract] |
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