Kinematic Slowing and Electrostatic Guiding of KBr Molecules Formed by the Reactive Collision Process: K + HBr → KBr + H

Abstract

We have generated a beam of translationally cold KBr molecules formed by exoergic reactive collisions in counterpropagating beams of K atoms and HBr molecules. The method relies on the extreme mass ratio of the products and the proper choice of the beam velocities (Liu, N.-N.; Loesch, H. J. Phys. Rev. Lett. 2007, 98, 10300). Here, we report the results of experiments on guiding the slow molecules from the site of their creation to the detector by a linear electrostatic quadrupole field. The device enhances the total intensity by a factor of 2.3 and the intensity at 14.2 m/s (1.4K) by an order of magnitude. The density velocity distributions, deduced directly from the observed time-of-flight profiles, peak at 20 m/s (2.9K). A numerical simulation of the guiding efficiency indicates that the polarization of the nascent molecules is first altered by a sudden change of the quantization axis from parallel to the initial relative velocity to parallel to the fringing field and thereafter follows adiabatically the local field as quantization axis. Drastic differences between the velocity and rotational state distributions of the molecules entering and leaving the energized quadrupole field are predicted. The counterpropagating beams can be used to continuously load an electrostatic trap. The equilibrium density of confined molecules is estimated to 1 x 10(7) cm(-3).