Bulletin of the American Physical Society
2018 Annual Meeting of the APS Mid-Atlantic Section
Volume 63, Number 20
Friday–Sunday, November 9–11, 2018; College Park, Maryland
Session G01: Chemical Physics III |
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Chair: Amy Mullin, University of Maryland, College Park Room: Edward St. John 1215 |
Saturday, November 10, 2018 4:00PM - 4:36PM |
G01.00001: Exploring uncharted regions of atmospheric reaction pathways Invited Speaker: Marsha I Lester Alkene ozonolysis is a primary oxidation pathway for alkenes, the most abundant organic compounds in the Earth’s troposphere after methane, and also an important source of atmospheric hydroxyl radicals (OH). Alkene ozonolysis takes place through a complicated reaction pathway with multiple intermediates and barriers along the way to OH products. A carbonyl oxide species, known as the Criegee intermediate (RR'COO), represents a critical branching point on the pathway that controls the products formed in this important class of reactions. Recent studies have focused on characterizing Criegee intermediates utilizing infrared and ultraviolet spectroscopic methods, and examining their unimolecular and bimolecular reactions under laboratory and atmospheric conditions. |
Saturday, November 10, 2018 4:36PM - 4:48PM |
G01.00002: State-Resolved Energy Profiles of Transient Sulfur Monoxide Radical: Photofragments from Sulfur Dioxide UV Photodissociation Paul B Diss, Christopher R Lukowski, Andrew J Pommersheim, Amy S Mullin The photodissociation dynamics from vibronically excited SO2 (C state) molecules give insight into possible mechanisms of photochemically-induced sulfur isotope effects seen in the early earth rock record. Photochemistry of SO2 is investigated using tunable, pulsed UV light (λ=210-225 nm) and state-resolved high-resolution transient IR absorption spectroscopy. Tunable UV light initiates dissociation and the photofragments are probed with 4.4 µm (2230-2300 cm-1) light. Individual Doppler-broadened ro-vibrational probe transitions and emission intensities were measured to determine UV-dependent dissociation quantum yields, nascent translational energy distributions, dissociation anisotropies, and rotational energy distributions. Measurements near the photodissociation threshold shed light on the dynamics of predissociative states resulting from non-adiabatic coupling. UV-wavelength-dependent studies of product energy partitioning were performed to characterize the dissociation mechanism from the electronically excited C state of SO2. |
Saturday, November 10, 2018 4:48PM - 5:00PM |
G01.00003: Multi-Harmonic Wavelength Modulation Spectroscopy for the Detection of Atmospheric Methane and Nitrous Oxide in mid-IR region May H Hlaing, Caio Azevedo, Amir Khan A high precision and sensitive wavelength modulation spectroscopy (WMS) multi-harmonic detection technique has been utilized in various fields including chemical sensing for environment, defense and industrial applications. The multi-harmonic WMS is an important tool to probe weak molecular rotational-vibrational transitions of overlapping atmospheric line transitions to determine atmospheric broadening, density etc. In this paper, we present quantum cascade laser based multi-harmonic WMS detection to simultaneously probe atmospheric broadened transitions of methane (CH4) and nitrous oxide (N2O) in the mid-infrared region (7.8 μm) of the spectrum. We show that for a given experimental SNR, the spectral line resolution of disparate line transitions can be improved by higher harmonic WMS detection. We also show that Rayleigh resolution criterion can be extended to quantify spectral resolution and the structures of WMS signals. |
Saturday, November 10, 2018 5:00PM - 5:36PM |
G01.00004: Electronic State Coupling in the Photofragmentation of the SH molecule Invited Speaker: Millard H. Alexander Absorption of a photon can rupture a diatomic hydride, either directly, or through predissociation of a bound electronic state. The non-hydrogen fragment can appear in several fine-structure levels. The relative population of these atomic levels can reveal information about the coupling between the several repulsive states as the atoms recede. We present an ab initio study of the SH(X2Π)→ SH(A2Σ+)→S(3PJ)+H reaction. We determined potential energy curves (PEC's) for the bound X and A states, and for the repulsive 2Σ–, 4Σ–and 4Π states, as well as the relevant spin-orbit coupling between the 18 individual states which correlate with S(3PJ)+H. A sophisticated time-independent method was used to simulate the photodissociation. We shall compare our theoretical predictions with existing experimental results from the groups of Zhang (Riverside), Orr-Ewing (Bristol), and Parker (Nijmegen),
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Saturday, November 10, 2018 5:36PM - 5:48PM |
G01.00005: Investigating the Collision Dynamics of CO Super Rotors in the Single-Collision Regime Tara J Michael, Hannah M Ogden, Amy S Mullin The dynamics of optically centrifuged CO molecules is investigated for the J = 29 – 68 rotational levels. An optical centrifuge is used to prepare an ensemble of CO molecules with oriented angular momentum in extremely high rotational states. High resolution transient IR absorption spectroscopy measures the state-resolved collision dynamics as the ensemble rotationally relaxes to thermal equilibrium. Implementation of a new multi-pass IR configuration in the experimental set-up has substantially increased signal-to-noise levels relative to previous single-pass measurements. It is now possible to observe population in rotational states associated with the nascent centrifuged distribution. Here we report the initial distribution of centrifuged CO molecules and investigate the collision dynamics in the single-collision regime. The mechanism of super rotor energy transfer is revealed through polarization-sensitive spectroscopy and time dependent orientational anisotropy measurements. |
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