Physics Colloquium – Wei Kong

Solving Atomic Structures of Molecules and Nanoclusters Using Superfluid Helium Droplet Cooling and Laser Alignment

Wei Kong
Department Head & Professor, Department of Chemistry – Oregon State University

We are building a prototype experimental apparatus to determine the atomic structures of molecules and nanoclusters using electron diffraction. We use superfluid helium droplets for cooling, thereby achieving effective field-induced orientation and alignment of the sample species. Electron diffraction patterns from the chosen orientation can then be accumulated until a satisfactory signal-to-noise ratio can be obtained. Changing the polarization of the laser changes the orientation of the sample species, hence three-dimensional structures can be obtained from the diffraction patterns of all orientations. The electrostatic potential of the sample species is derived using the oversampling method for iterative phase retrieval and structure determination. We demonstrate the apparatus’s performance using atomic and molecular clusters, with the ultimate goal of solving macromolecular structures, such as proteins, from an electrospray ionization mass spectrometer. Examples of our recent progress will be discussed, leading to insights of cluster formation in the unique environment of superfluid helium droplets.