Ultracold molecules are a promising platform for diverse scientific goals, ranging from quantum information and simulation to controlled chemistry and precision measurements of fundamental physics. The rich internal structure of molecules, including vibrations, rotations, and hyperfine interactions, provides many handles for exquisite control. However, the very same structural features that make molecules so desirable to study also complicate the task of controlling a molecular species. Recently, laser cooling and magneto-optical trapping of diatomic molecules has been realized by several groups around the world, leading to temperatures as low as a few μK in long-lived, trapped samples of CaF. The ability to laser cool also allows for high fidelity detection of ultracold molecules and increases in phase space density allowing, e.g., the study of ultracold molecular collisions. As our group has shown with SrOH, these cooling methods apply to a broad and generic class of molecules, including polyatomic species which offer significant and qualitatively new advantages over any diatomic species. For example, polyatomic molecules may be fully polarized at extremely low electric fields and provide longer coherence times, allowing one to probe physics Beyond the Standard Model at the PeV scale. Importantly, the presence of these additional states in polyatomics does not interfere with the laser cooling process already observed in simpler species. In this talk, I will outline the experimental goal of creating ultracold gases of polyatomic molecules using illustrative examples from our laser cooling of CaF and SrOH molecules. I will also present how we will extend the techniques already demonstrated to chiral molecules, whose asymmetry presents novel challenges but also exciting new possibilities.

Characterization of protein structures at interfaces in situ and in real time is important to solve fundamental and engineering problems. Nonetheless, such characterization remains challenging because it requires methods to be both selective to interfaces and protein structures. We show that chiral vibrational sum frequency generation spectroscopy (SFG) can provide peptide amide I and N-H stretching vibrational signals that are free of water background and characteristic to parallel beta-sheet, anti-parallel beta-sheet, alpha-helix, 3-10 helix, and disordered structures, thus enabling characterization of protein secondary structures at interfaces, similar to circular dichroism for characterizing protein structures in solution. Using chiral SFG, we monitor misfolding of an amyloid protein, measure interfacial protein orientation, derive new methods for probing backbone proton exchange, and examine two-dimensional crowding effects on protein folding. Moreover, we observe chiral SFG stretching modes of water molecules associated with a beta-sheet protein. This result reveals that achiral water molecules can be organized by the protein into chiral supermolecular structures. The result also implies that chiral SFG can be a promising vibrational probe for water structures in protein hydration. These recent developments demonstrate that chiral SFG can provide an array of new tools for addressing biological and biomedical problems related to protein structures.

Among different spectroscopic techniques, rotational spectroscopy, given its intrinsic high resolution and high sensitivity, is one of the most powerful tools for investigating the structure and dynamics of molecules and supramolecular systems in the gas phase. Rotational spectra contain a wealth of accurate information on structural, molecular, and spectroscopic parameters that are difficult or impossible to obtain by other experimental techniques. However, the task of extracting information from the analysis of the spectral features is challenging, time-consuming, and prone to errors. In the last decade, rotational spectroscopy has experienced huge technological improvements that have led to a revitalization of the field, also due to parallel advancements in theoretical methods and computational resources. Given these advances, the interplay of theory and experiment in rotational spectroscopy is discussed by means of representative examples that vividly illustrate what can be accomplished with theory and experiment brought together in this field. In particular, it will be shown how such an interplay can be exploited to address new challenges, exemplified by studying the nature of weak interactions in molecular adducts where the bonding pairs are made up of non-hydrogen atoms. Another fascinating challenge is offered by the open issues posed by astrochemistry. Astronomical observations of rotational spectroscopy signatures provide the unequivocal proof of the presence of chemical species in the astronomical source under consideration, and the talk will also explore the degree to which rotational spectroscopy can assist in going beyond the "simple" identification of interstellar species.

At the Missouri University of Science and Technology we are interested in developing tools and techniques to obtain new understanding and disseminate knowledge about molecular rotational spectra. We accomplish these ends by researching new ways to attack microwave spectroscopic problems both in the research and teaching laboratories. Some of the problems we are interested in involve providing research-grade microwave teaching tools to students with limited financial resources, O₂ van der Waals complexes and the complexities of spin coupling, and trying to identify new approaches for chiral molecule analysis using the microwave technique. Because many of our spectroscopic studies employ the CP-FTMW technique, we are also developing methodologies to improve the sensitivity of this instrument through instrumental design. This talk will provide a brief overview of each of these topics and some of the progress we have made. L0pt      

Nanostructured particles hold much promise as "designer materials,” but full realization of this promise requires a detailed understanding of the geometric and electronic effects driving their behavior. While some smaller particles, often called nanoclusters, can be synthesized monodispersely and crystallized to determine their geometric structures, this is not generally true and no similarly powerful technique exists for the determination of their electronic structures. We have extended mass-selective action spectroscopy techniques to small ligand-protected metal nanoclusters synthesized using standard solution-phase protocols. These clusters are mass-selected from a mixture and stored in a variable-temperature ion trap where they adsorb weakly-bound "tag” molecules that act both as action spectroscopy messengers and a mildly perturbative environment. These experiments reveal dramatically more information than do typical UV/Vis spectra in solution, likely at the limit of resolution considering lifetime effects and the high density of states of the clusters. We find that minor functionalization of the protecting ligands has a drastic impact on the cluster electronic structure, even for transitions between two nominally metal-based states. Even more surprisingly, very subtle environmental effects, such as solvation by He or N₂, yield notable shifts to the spectra, suggesting that even weakly interacting ligands and solvents can have major effects. Taken together, these spectra provide the first experimental windows into using subtle chemical effects to tune the properties of these clusters for chemical and technological applications.