Electron Diffraction of Molecules in Superfluid Helium Droplets Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/8k71nn54t

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  • In this dissertation, I describe the experimental investigation in electron diffraction of molecules in superfluid helium droplets. The project is part of an overall scheme called ‘single molecule serial electron diffraction imaging’ (SS-EDI), with the ultimate goal of building an apparatus to determine atomic structures from oriented macromolecules. In SS-EDI, protein ions are doped in helium droplets and the doped droplets are then oriented by an elliptically polarized laser and exposed to a coherent electron beam for diffraction. The specific goal of my project is to explore the feasibility for electron diffraction of molecules in helium droplets. I started by installing several diagnostic components and systematically characterizing the behavior of the helium droplet beam, including its timing profile, size distribution, and doping statistics. I then moved on to electron diffraction of molecules in helium droplets. In the work on CBr4, the background issue from helium atoms was solved by increasing the doping path length or pressure of gaseous CBr4. In the experiment of ferrocene, the velocity slip of our pulsed droplet beam has been utilized to separate different sized droplets and to achieve efficient single doping in one droplet. The resulting success testifies to the capability of size control of our experiment. In the work of I2, the investigation was further expanded to different sized droplets containing different sized iodine clusters. From this study, we observed for the first time halogen bonded iodine clusters and bi-layer iodine nanocrystals. The work in this dissertation represents a major step in demonstrating the working principle of the overall idea of SS-EDI. The successes of these efforts imply that by embedding the sample in a superfluid helium droplet, the structurally relevant diffraction information of the sample can still be retrieved, as long as one can control the amount of helium surrounding the sample.
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  • description.provenance : Approved for entry into archive by Steven Van Tuyl(steve.vantuyl@oregonstate.edu) on 2017-06-12T23:01:25Z (GMT) No. of bitstreams: 1HeYunteng2017.pdf: 4056959 bytes, checksum: c843ac334c19637155bc79a4d9ccd44f (MD5)
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