Tags: Physical Seminar


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…


Photochemical Synthesis and Spectroscopy of Polycyclic Aromatic Hydrocarbon Dimers

Laser desorption time-of-flight mass spectrometry (LD-ToF-MS) experiments on pressed-pellet samples of polycyclic aromatic hydrocarbons (PAHs) produce covalently-bonded dimers at masses (m/z) of 2M-2 and 2M-4 (where M is the parent mass). Through replication of these LD-ToF-MS conditions at higher throughput, PAH dimers have been produced and collected in milligram quantities. For collected samples of pyrene, perylene, and coronene,…


Experimental Catalyst Design Aided by Machine Learning

In the past, catalyst design has been highly characterized by trial and error based on previous experience and knowledge of catalysis.1 Due to the number of variables involved in catalyst performance, it is difficult to manually optimize highly active catalysts. In the past few years, there has been a movement toward the use of machine learning as a tool in experimental catalyst design. There have been numerous studies published using different…


Insights Into Molecular Structure Via Atomic Force Microscopy

Accurately characterizing the structure of molecules is a fundamental goal for chemists. Many powerful techniques exist to do so (e.g. NMR, IR Spectroscopy, X-ray Crystallography, etc.) and have proven themselves to be extremely effective. However, there are certain cases where these standard ensemble methods struggle to characterize certain systems. In 1986, Binning and coworkers developed Atomic Force Microscopy (AFM) as a complementary method…


Coupled Cluster Externally Corrected by Adaptive Configuration Interaction

An externally corrected coupled cluster (CC) 1 method, where an adaptive configuration interaction (ACI) 2,3 wave function provides the external cluster amplitudes, named ACI-CC, was presented. By exploiting the connection between configuration interaction and coupled cluster through cluster analysis, the higher-order T3 and T4 terms obtained from ACI are used to augment the T1 and T2 amplitude equations from traditional coupled cluster. These…


Gaseous SO2 and H2O Droplets: A Deep Dive Into Surface-level Interactions

The interactions between gaseous SO2 and the surface of water droplets have been studied extensively over the years due to the environmental impacts of aerosols. Spectroscopic methods including vibrational sum-frequency spectroscopy (VSFS) have been used to better understand the mechanism in which gaseous SO2 reacts and dissolves on a water droplet surface1-3. A weakly bonded SO2:H2O complex on the surface of water droplets has been observed…
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