Molecular Rydberg Spectra Encode Intramolecular Dynamics

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Molecules typically contain many electrons, and, being negatively charged, these electrons repel each other as they move in space. Electron-electron repulsion makes it difficult to calculate precisely the properties and behaviors of molecules, and remains one of the greatest challenges for the science of chemistry. With the support of the Chemical Structure, Dynamics and Mechanisms-A Program of the Division of Chemistry, Professor Robert Field and his research team at the Massachusetts Institute of Technology are using advanced laser and microwave spectroscopy techniques to prepare and interrogate what are called Rydberg molecules. A Rydberg molecule is a normal molecule in which one electron has been excited (by laser light) to such a high orbit that the system resembles a simple hydrogen atom (one negatively charged electron plus one positively charged proton). Because of their simplicity, Rydberg molecules can be modeled more accurately with theory, and it becomes possible to answer other questions with more accuracy, for example, how do electrons interact with light? Or how do electrons exchange energy with each other and with the positive-charged "ion core" of the molecule? This research project challenges conventional thinking about the structure of molecules and how they interact with light. The discoveries from this project may also have implications for the new field of quantum computing. The post-doctoral scientists and undergraduate researchers engaged in this project are gaining experience in both cutting-edge laser/microwave technology and computational chemistry. This project is focused on three experimental goals and targeted at answers to three fundamental questions. The feasibilities of the principal experimental components have been independently demonstrated. The experimental goals are: (i) to record Rydberg-Rydberg spectra at a spectral velocity of 100,000 resolution elements per second, organized and assigned by a suite of on-the-fly diagnostics; (ii) to exploit systematic spectroscopic access to core-nonpenetrating Rydberg states, bypassing a region of fast nonradiative decay previously deemed to be impassible (called the "zone of death"); (iii) to exploit superradiance on Rydberg-Rydberg transitions to obtain information about quantum many-body interactions. If these experiments are successful, our methods and results will challenge spectroscopists to imagine and target new frontiers for the spectroscopy of gas phase molecules. This project is leading to new methods for the determination of multipole moments an polarizabilities of molecular-ions, which are essential to model dense plasmas, which are relevant to astrophysics and new technologies. The refinement of Multi-channel Quantum Defect Theory promises a priori calibrated methods for production of state-selected molecular ions devise new classes of schemes for external control of molecular dynamics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.