Phys Chem/Chem Phys Seminar

Over the last 20 years, we have discovered that we live in a molecular Universe: A Universe with a rich and varied organic inventory; A Universe where molecules are abundant and widespread; A Universe where molecules play a central role in key processes that dominate the structure and evolution of galaxies. A Universe where molecules provide convenient thermometers and barometers to probe local physical conditions.

Abstract: Modeling gas-phase chemical kinetics relevant to combustion and atmospheric chemistry requires a complete description of elementary reactions involving ephemeral species such as hydroperoxyalkyl radicals, Q̇OOH, which undergo competing sets of unimolecular reactions and bimolecular reactions with O2. The balance of flux from the competition affects rates of chain-branching and inherently depends on temperature, pressure, and oxygen concentration.

Quantum interferences, where two electronic pathways “compete” in a manner akin to the interference of separate propagating waves, are often exploited in atomic systems to realize a variety of exotic phenomena, such as electromagnetically induced transparency, slow light and lasing without inversion. In crystalline materials, quantum interferences can sometimes be difficult to discern with conventional probes, even if their consequences may be just as profound.

Mid-Infrared (MIR) light can interact with molecules by selectively exciting molecular vibrational modes. In combination with photonic structures, MIR can target specific vibrational states of molecular to influence chemical reactions. In this talk, I will explain how photonic environments can modify molecular dynamics through strong light-matter coupling. This strong coupling leads to the molecular vibrational polaritons – a hybrid quasiparticle between light and matter.

Control of spin and valley polarizations opens opportunities for spintronic and quantum information applications. Monolayer transition-metal dichalcogenides (TMDs) offer an appealing platform to harness such polarizations. TMDs host excitons in valley-shaped regions of their band structure, featuring well-defined carrier spins and obeying chiral optical selection rules. However, the technological potential of excitons in TMDs is impeded by rapid spin–valley relaxation.

Abstract: Non-methane volatile organic compounds (NMVOC) are emitted into the Earth’s atmosphere by varied biogenic and anthropogenic sources. Though the concentrations of these compounds are minute, they exert an outsized influence on atmospheric composition, primarily through their oxidation chemistry. This chemistry leads to the formation of key secondary species including tropospheric ozone, a harmful pollutant, and secondary organic aerosol (SOA), a key component of atmospheric particulate matter with implications for climate and air quality.

Abstract: Polaritons are hybrid light-matter states with unusual properties that arise from strong interactions between a molecular ensemble and the confined electromagnetic field of an optical cavity. Cavity-coupled molecules appear to demonstrate energetics, reactivity, and photophysics distinct from their free-space counterparts, but the mechanisms and scope of these phenomena remain open questions. I will discuss new experimental platforms that the Weichman Lab is developing to investigate molecular reaction dynamics under strong cavity coupling.

Abstract: My talk will highlight new directions in probing semiconductor electrochemistry and reactivity at the single-particle and single-molecule level. I will discuss our recent discovery that the band gap renormalization (BGR) effect in 2D semiconductors strongly dictates their current–voltage behaviorin electrochemical cells, providing a new framework to understand solid-state transistor device performance variability.

Abstract: Proteins operate within an aqueous environment that influences their folding, stability, and activity. Membrane proteins have the added complication of being embedded in lipid bilayers that play an equally critical, yet significantly less understood, role. Much like solvent conditions modulate enzyme kinetics and protein interactions in solution, the lipid composition of the membrane performs regulatory functions for membrane proteins, affecting their organization, conformational dynamics, and catalytic output.