Graduate Thesis Or Dissertation


Properties of Large Superfluid Helium Droplets Public Deposited

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  • In this dissertation, I describe the experimental investigation of large superfluid helium droplets. The goal and direction of this thesis is to facilitate the use of these droplets as part of our project ss-EDI. The overall scheme of ss-EDI is to dope proteins inside helium droplets and collect a diffraction image of the doped droplets after orienting the dopant using elliptically polarized light. Doping the macromolecules requires the use of relatively bigger helium droplets to study protein structures. We have succeeded in using the droplets we generate in our lab to carry GFP ions generated from electrospray ionization source. The generated droplets were extremely big which raised the question of the effect of these droplets on the dopant interaction with any external field. For this reason, we have carried other experiments using R6G+ ions generated through electrospray ionization and doped to helium droplets. The goal of this experiment is an attempt to eject the dopant ion while still achieving low internal temperature to try to reduce the noise from helium droplets in the diffraction image. An attempt that was not as successful as desired due to low ejection yield that is related to the large size of helium droplets which opposes constrains on the escape of the ions. This has sparked the need to fully investigate large helium droplets using simpler dopants like aniline. Ionizing Aniline through electron impact ionization and then using photoexcitation to eject the dopant ions revealed unique properties of the large superfluid helium droplets like caging effect on the dopant and the ability to carry several ions or different species. Properties that stem from the resemblance of large droplets to the bulk properties unlike the smaller helium droplets that represent surface layers of the droplets.
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