Beam Deflection Studies of Cold Molecules and Complexes Entrapped in Helium Nanodroplets: Permanent, Metastable, and Laser-Induced Electric and Magnetic Dipole Moments

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In this project, supported by the Chemical Structure, Dynamics, and Mechanisms (CSDM-A) Program of the Division of Chemistry, Prof. Vitaly Kresin’s group at the University of Southern California will study the distributions of electrical charges and magnetic currents within extremely cold molecules carried by a beam of nanoscale droplets of superfluid helium. These distributions reveal information about molecular structure, motion, and bonding. The nanodroplets will pass through an externally applied electric or magnetic field, and the field-induced deflection of their trajectories will be measured. The study will encompass the electric and magnetic structure of biological molecules, atomic and molecular complexes, “molecular magnets,” and other systems that are impractical to accurately measure, or even synthesize, by other means. The project also will demonstrate steering of a molecular reaction by an external electric field and detecting the switching of the electric polarity of a molecule by a tunable laser. The project will lead to new knowledge that has broad relevance to basic research and applications ranging from protein formation to ultracold chemistry, spintronics to organic synthesis, and atmospheric chemistry to quantum information science. Graduate and undergraduate students will be mentored in a highly interdisciplinary research field and engage in science fairs and school outreach programs. A collaboration between the project and an undergraduate laboratory course in combinatorial chemistry will be established.The nanodroplets, formed via supersonic expansion of helium gas, will embed molecules, atoms, or clusters from vapor in pick-up cells, and then traverse a strong inhomogeneous electric or magnetic field. This field will orient the ultracold polar impurities and exert an intense deflecting force, resulting in a measurable deviation of the beam, thus enabling direct readout of the electric or magnetic dipole moment of the molecule or complex. This technique will be applied to hydrogen peroxide clusters, amino acid dimers and dipeptides, high-spin alkali dimers, and molecular magnets. Furthermore, the project will demonstrate the assembly of pre-oriented molecules, and deflection-based action spectroscopy of photochromic molecules.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.