Tags: Physical Seminar


Four Isomers of In2H2: a Careful Comparison Between Theory and Experiment

Four constitutional isomers of diindium dihydride have been studied utilising rigorous quantum mechanical methods. Geometries were optimised with the CCSD(T) method using the aug-cc-pwCVTZ basis set and a small-core pseudopotential for the indium atoms. Relative energetics were determined at the CCSD(T)/CBS level of theory, and the higher order δT(Q) contributions are also computed. The monobridged and vinylidene-like isomers lie 10.8 and 13.6 …


The Many-Body Expansion in Chemistry

The Many-Body Expansion (MBE) of the energy of a chemical system is a powerful tool that encodes physical descriptors of cooperative effects in chemical systems. Depending on the definition of what a “body” is, the expansion can be applied to a wide variety of chemical ensembles. When applied to hydrogen bonded systems, such as water and aqueous ionic clusters including ions in the Hofmeister series, it has direct implications in the development…


HENDI Spectroscopy of the Butyl Radicals

Butyl radicals (n-, s-, i-, and tert-butyl) are formed from the pyrolysis of nitrite or azo- precursors. The radicals are doped into a beam of liquid helium droplets and probed with infrared action spectroscopy from 2700−3125 cm-1, allowing for a low temperature measurement of the CH stretching region. The presence of anharmonic resonance polyads in the 2800 − 3000 cm-1 region complicates its interpretation. To facilitate spectral assignment,…


Development of Sub-Mechanisms for Cyclic Ethers: Alkyl-Substituted Oxiranes

Oxiranes are a class of cyclic ethers formed in abundance during the low-temperature combustion of hydrocarbons and biofuels from the unimolecular decomposition of hydroperoxyalkyl radicals (Q̇OOH). For example, ethyloxirane, cis-2,3-dimethyloxirane, and trans-2,3-dimethyloxirane are produced as intermediates during the oxidation of n-butane. While rate coefficients for the unimolecular decomposition of Q̇OOH to the aforementioned species are…


A Helium Nanodroplet Instrument for Infrared Spectroscopy of Molecular Ions

Helium nanodroplets provide a cold, inert, and optically transparent environment for doping atomic and molecular species. Helium's weak interaction with dopants is minimally perturbing, and facilitates the collection of high-resolution vibrational and rotational spectra. An instrument was designed that facilitates the ionization of dopant molecules using resonant two-photon ionization. Excitation of the molecular ions then occurs using a tunable…


Shocks on a Benchtop: The Study of Shocked Energetic Materials with Ultrafast Dynamic Ellipsometry

Shock waves travelling through a material generate incredible amounts of pressure and cause irreversible changes in said material. Observing mechanical and chemical changes in an energetic material under shock is of particular interest in the study of detonations. Until recently, most experimental measurements of shock waves and shock induced chemistry have been limited to the nanosecond scale. Ultrafast Dynamic Ellipsometry (UDE) is a single-…


Machine Learning Methods for Studying Complex Potential Energy Surfaces

For complex molecular systems, computational methods can provide fine details that are not readily available from experimental methods. However, some insight can only come from thorough exploration of the potential energy surface (PES) for a molecular system. Exhaustive PES exploration using quantum mechanical methods is very time- and resource-consuming. Empirical reactive force fields can provide a more cost-effective alternative to quantum…


Examining Cyclic Ether Consumption in Low-Temperature Oxidation

Oxiranes are a class of cyclic ethers formed in abundance during low-temperature combustion of hydrocarbons and biofuels. While rate coefficients for the formation of 2,3-dimethyloxirane are reported extensively, subsequent reaction mechanisms of the cyclic ether are not. As a result, chemical kinetics mechanisms commonly adopt simplified chemistry to describe the consumption of 2,3-dimethyloxirane, which may introduce mechanism truncation error…


Extracting Kinetic Data from Reactive Molecular Dynamic Simulations

Reactive molecular dynamics (RMD) is a branch of molecular dynamics in which chemical reactions can be simulated. This is made possible by a special group of force fields (e.g. ReaxFF) which allow for dynamic bond orders to be calculated as a function of bond distance. RMD simulations are particularly useful in situations where experiment would be too difficult or expensive to justify without some indication of success. They can also serve to…


Attosecond Transient Absorption “Spooktroscopy”: Using entanglement to overcome spectral instability in Xray Free Electron Lasers

X-ray Free Electron Lasers (XFELs) produce high intensity X-rays with attosecond pulse durations by “undulating” an electron beam at high speeds. The generation of these X-ray pulses allow for Attosecond Pump-Probe Spectroscopy to be used on dilute, gas phase samples. However, XFELs have a problem with shot to shot spectral variation, and due to this, they are not well suited to absorption measurements. To combat this, researchers at the…
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