Dynamics of neutral molecules stored in a ring

A decelerated beam of neutral ammonia molecules is injected into an electrostatic storage ring. Electrostatic lenses are used to map the emittance of the decelerator onto the acceptance of the ring. The tangential velocity spread of the package of molecules in the ring is set to less than 1 m / s. The package of molecules can be observed for more than 50 distinct round trips, corresponding to 40 m in circular orbit and almost 0.5 s storage time, sufficiently long for a first investigation of its transversal motion in the ring. Getting full control over both the internal and external degrees of freedom of molecules has been an important goal in molecular physics during the past decade. This control can be achieved, in principle, with appropriately tailored electromagnetic fields [1,2]. Radiation fields can be used, for instance, to prepare molecules in a single selected quantum state, thereby controlling their electronic, vibrational, and rotational degrees of freedom. Static inhomogeneous electric and magnetic fields have been used for a long time to (de)focus polar molecules in a beam, thereby manipulating their transversal position and velocity and controlling their orientation [3]. Time-varying electric fields can be used to efficiently change the forward(longitudinal) position and velocity of these molecules as well [4,5]. In the experiments reported here, a package of ammonia molecules in a single rovibrational state, spatially oriented, is decelerated and focused and subsequently forced in circular orbits. The absolute velocity, as well as the width of the velocity distribution, of the package of molecules is under computer control, and these experiments thereby serve as a demonstration of the level of control over neutral molecules that can nowadays be