Spectroscopic studies of van der Waals interactions, cluster containing transient intermediates, and development of Mid IR nano-sensors

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This proposal focuses on three areas in molecular/chemical physics. First, we will conduct experimental and theoretical studies of noncovalent bonds between atoms and molecules. Noncovalent bonds are orders of magnitude weaker than chemical bonds but act over a much longer range and have profound influence over many chemical and biological systems. They are responsible for collisional effects in gases, aerosol formation, bulk properties of water, the secondary and tertiary structures of proteins and the double helix structure of DNA to name a few. Noncovalent interactions are governed by the electronic structure of the interacting molecules which in principle can be treated using the Schrodinger Equation (SE). However, the exact solution to this equation is impossible because of the electron correlation problem. In its simplest form the SE consists of kinetic and potential energy terms. While the kinetic energy is straightforward to calculate, computation of the PES is a nontrivial task. We will use the synergy between experiment and theory to develop potential energy surfaces (PESs) with ever increasing levels of sophistication and accuracy. The PES serves as a defining part of the SE and the essential ingredient for spectroscopic or dynamical study of molecular clusters. The emerging high-accuracy PESs can be tested against our spectroscopic observables. Second, we are interested in laboratory data in the form of line parameters and absorption cross-sections for remote sensing of hydrocarbons. For example, because ethane is the second most abundant hydrocarbon (after methane), laboratory data are required to study the methane cycle in the atmospheres of outer planets. Other uses of our data include transmission simulations, industrial process monitoring, and pollution regulatory studies. We will focus on development of quantum mechanical models for frequency and intensity of the mid-IR bands of ethane. The line parameters can then be used to compute a spectrum at an arbitrary temperature and pressure to cover the physical conditions encountered. Lastly, the mid-IR contains the strong absorption signatures of many greenhouse gases that are of extreme interest in sensing applications. The miniaturization of spectroscopic sensing equipment made possible by engineered silicon photonics has the potential to revolutionize sensing in the mid-IR. Advances in materials engineering have shown that silicon-based photonic devices can support optical propagation in the mid-IR with losses approaching those of the telecommunications band, making the region attractive for nanoscale sensor development. We will develop sensitive, compact, portable, and low-cost sensors for monitoring greenhouse gases to be used on unmanned aerial vehicles. The outcomes of the proposed research hold answers to key questions asked in cluster and aerosol science, in astronomy and by scientists with interest in climate change, remote sensing, and industrial control process.