The primary objective of this project is to advance the understanding of physical and chemical processes that drive molecular bond cleavage and formation at plasma-liquid interfaces. Specifically, the research aims to develop and implement new in-situ diagnostic techniques based on multiple internal reflection spectroscopy to study plasma-liquid interactions involving water and organic liquids. The project will use some of the key diagnostics such as Attenuated Total Internal Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Attenuated Multiple Total Internal Reflection Optical Spectroscopy (AMTIR-OS) to detect and study species at the plasma-liquid interface, and Rayleigh Scattering to measure gas temperature, optical emission spectroscopy to measure plasma species, electron density from Stark broadening and Thomson Scattering to measure electron density and temperature. The proposed research will use the Princeton Collaborative Research Facility resources for Rayleigh and Thomson Scattering experiments. The key innovation of this project will be the introduction of total internal reflection spectroscopy to the existing arsenal of plasma diagnostics used to study plasma-liquid systems. Various methods will be attempted to create thin liquid films or layers on Attenuated Total Reflectance (ATR) crystals, such as hydrogels, microcrevices, and surface treatments to resolve and detect species within nanometers to microns of the plasma-surface interface. Species and energy transport in the plasma and liquid phases will be modeled to support and interpret experimental observations. Specifically, the research will explore plasma-liquid interactions for three systems: (i) Ar-water, (ii) Ar/N2-water, and (iii) Ar-liquid alkanes and alkenes. Model alkanes such as decane and decene that approximate polymer melts will be used to inform future applications such as polymer recycling.