New Experimental Platforms for Molecular Polaritonics

Marissa Weichman Princeton University, Department of Chemistry

Polaritons are hybrid light-matter states that arise from strong interactions between a molecular ensemble and the confined electromagnetic field of an optical cavity. Cavity-coupled molecules appear to demonstrate chemical behavior distinct from their free-space counterparts, but the mechanisms and scope of these phenomena remain open questions [1]. I will discuss new experimental platforms that the Weichman Lab is developing to investigate molecular reaction dynamics under vibrational strong coupling.

While polaritons are now well-established in solution-phase and solid-state systems, they had not been previously reported in gas-phase molecules, where attaining suLiciently strong light-matter interactions is a challenge. We access the strong coupling regime in an intracavity cryogenic buLer gas cell optimized for the preparation of cold, dense ensembles and report a demonstration of strongly coupled rovibrational transitoin in gas-phase methane [2,3]. In ongoing work, we will harness this infrastructure as a new testbed for fundamental studies of polariton physics and chemistry [4].

We are also searching for signatures of cavity-altered dynamics in benchmark solution-phase systems [5,6]. So far, we have focused on radical hydrogen-abstraction processes, which have well- characterized reactive surfaces and can be initiated with photolysis and tracked directly on ultrafast timescales. We use ultrafast transient absorption to examine intracavity reaction rates with the goal of better understanding exactly how and when reactive trajectories may be influenced by strong light-matter interactions.

[1] K. Schwennicke, A. Koner, J. B. Pérez-Sánchez, W. Xiong, N. C. Giebink, M. L. Weichman, and J. Yuen-Zhou. When do molecular polaritons behave like optical filters? arXiv 2408.05036 (2024).

[2] A. D. Wright, J. C. Nelson, and M. L. Weichman. Rovibrational polaritons in gas-phase methane. J. Am. Chem. Soc. 145, 5982 (2023).

[3] A. D. Wright, J. C. Nelson, and M. L. Weichman. A versatile platform for gas-phase molecular polaritonics. J. Chem. Phys. 159, 164202 (2023).

[4] J. C. Nelson and M. L. Weichman. More than just smoke and mirrors: Gas-phase polaritons for optical control of chemistry. J. Chem. Phys. 161, 074304 (2024).

[5] A. P. Fidler, L. Chen, A. M. McKillop, and M. L. Weichman. Ultrafast dynamics of CN radical reactions with chloroform solvent under vibrational strong coupling. J. Chem. Phys. 159, 164302 (2023).

[6] L. Chen, A. P. Fidler, A. M. McKillop, and M. L. Weichman. Exploring the impact of vibrational cavity coupling strength on ultrafast CN + c-C6H12 reaction dynamics. Nanophotonics 13, 2591 (2024).