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Abstract

Exploiting the Stark effect, neutral polar molecules can be focused and decelerated in an array of time-varying inhomogeneous electric fields in alternatinggradient configuration. Using this principle, a new experiment for the focusing and deceleration of large molecules from a molecular beam has been set up. With the new setup, the alternating-gradient focusing and deceleration of benzonitrile, a prototypical large molecule, have been demonstrated. Benzonitrile has been decelerated in its absolute ground state, which is not susceptible to inelastic collisions at sufficiently low temperatures, as well as in rotationally excited states.
Because of the complexity of the Stark manifold with a large number of real and avoided crossings, it was not a priori clear whether benzonitrile in excited rotational states could be decelerated. However, this has been successfully demonstrated in this thesis. Furthermore, using the same alternating-gradient setup, OH radicals in both low-field-seeking and high-field-seeking quantum states have been focused and decelerated. For the deceleration of molecules in a low-fieldseeking quantum state using an alternating-gradient decelerator, a new high voltage switching scheme has to be applied in order to achieve phase stability for the decelerated packets. In addition, the coupling of transverse and longitudinal motion in the alternating-gradient decelerator has been studied. All focusing and deceleration measurements agree well with the outcome of trajectory
simulations. The experiments performed in this thesis demonstrate that alternating-gradient focusing and deceleration is a general method: it allows to decelerate polar molecules in both low-field-seeking and high-field-seeking quantum states as well as in ground and rotationally excited states. Furthermore, it shows that large polyatomic molecules, eventually biomolecules, are amenable to the powerful method of Stark deceleration using time-varying inhomogeneous electric fields.