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Title: Electrodynamic guiding and deceleration of polar diatomic molecules
Author: Darnley, Richard Vincent Bernard
ISNI:       0000 0004 2674 3320
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2009
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This thesis reports on the properties of an alternating gradient guide and decelerator for heavy polar diatomic molecules, 179Yb19F and 40Ca19F, in the ground ro-vibrational and electronic state. A study of clustering was undertaken pointing to a link between cluster formation and the molecular beam intensity. A cold (-3 K) supersonic beam of CaF molecules was developed for these experiments. We studied the guiding properties of the Stark decelerator over a wide range of parameters. encompassing different voltages, molecular beam speeds and species. Transmission of molecules through the decelerator was compared with various theoretical predictions, and agreement was found only when a full 3-dimensional finite-element map of the electrostatic field of the lenses was considered. A localized strengthening of the defocusing force was found at the entrance and exit of the lenses. This defocusing field gradient, brought oil by the nonzero longitudinal gradient in the fringe fields, is an inherent property of our two-electrode lens design. A better, four-electrode lens geometry is suggested. A universal scaling, applicable to harmonic lenses, was found. This allowed direct comparison between all the experimental and simulated transmission data, and worked remarkably well even when anharmonic and fringe field effects were significant. Some residual discrepancies remain to be understood. YbF molecules have been decelerated, demonstrating an increased loss in kinetic energy (13cA) over previous published results, and for the first time, we have decelerated (accelerated) CaF demonstrating a 10% loss (gain) in kinetic energy. The deceleration data agree with the expected energy loss, and also demonstrate the effect of longitudinal bunching. We have observed and understood a further loss of transmission when molecules are strongly decelerated. This is due to a decrease of the confining potential in the axial direction. The proposed 4-electrode decelerator is expected to produce more decelerated molecules.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available