Understanding the Nature of Vibrational Strong Coupling in Small Molecules

Abstract

newline Abstract: Strong light-matter interaction resulting in the formation of hybrid light-matter states newline(polaritonic states) is one of the fastest-growing research areas. It has been demonstrated newlineexperimentally that the physical and chemical properties of molecules and materials can be altered by newlinestrong coupling. For example, chemical reactivity, supramolecular self-assembly, conductivity, newlinesuperconductivity etc., are modified at room temperature. However, the exact mechanism of the newlineprocess is still not clear. In order to comprehend the cause of these coupling-induced modifications, it newlineis therefore, crucial to explore thoroughly the behavior of newly generated polaritonic states. The newlinecurrent thesis aims to investigate the spectroscopic characteristics of these newly formed polaritonic newlinestates of small molecules in various phases. Firstly, an inhomogeneously broad OH/OD vibrational state newlineof water/heavy water is studied systematically using advanced infrared spectroscopic tool along with newlinetransfer matrix simulations. Water vibrational states can effectively generate polaritonic states as low newlineas 5% (v/v), and the photonic fraction persists even after detuning to a large range, indicating the newlineversatile use of the system for polaritonic chemistry experiments. Further, linear molecules like carbon newlinedisulfide with very high oscillator strength is studied. Our experimental and analytical modeling newlinesuggest that the self-dipolar interaction term is enhanced drastically in ultra-strong coupling newlineconditions. i.e., the actual absorption strength is boosted while coupling the oscillator to the vacuum newlinefield. The coupling strength is purely dependent on the orientation of the molecular dipoles with the newlineelectric field. Here, we used three small strained cyclic ketones (cyclobutanone, cyclopentanone, and newlinecyclohexanone) and probed the temperature-dependent vibrational strong coupling experiments. newlineFinally, gas phase molecules were also tested as they have the least molecule-molecule interactions. newlineRo-vibrational states of the gase