Spatial Taming and Trapping of Molecules

Harvard University, Cambridge MA

Investigators

Abstract

Dudley Herschbach is supported by the Experimental Physical Chemistry Program to develop an apparatus for manipulating and trapping molecules with very low translational energies. This will be accomplished by molecular beam expansion cooling of gases exiting from the periphery of a high speed contra-rotating rotor such that the rotortip motion cancels out the expansion velocity. There is also the option of increasing the velocity above thermal by co-rotating the rotor. The basic viability was established using Xe and the technique is being developed and extends to other gases (O2, Cl2, HCl and CO). Five developments being made are to: 1) improve the rotor construction and eliminate design weaknesses; 2) increase the pressure for the supersonic expansion to achieve lower temperatures; 3) improve the vacuum to reduce slow molecule scattering; 4) develop techniques for collecting the slow molecules and 5) use a pulsed gas nozzle to improve the uni-directional nature of the supersonic beam. In parallel with these developments, there are a) studies of chemistry at low temperatures, specifically that of OH, b) use of inhomogeneous static and laser fields to scatter or focus the slow particles and c) demonstrations of the de Broglie nature of the slow particles by molecular diffraction. The studies are developing a device in which molecules can be cooled down to very low temperatures, as low as one degree above absolute zero of temperature. At these temperatures, the molecules have speeds of a few tens of meters per second and have wavelengths large compared with their size. This entirely changes the nature of the reactive collisions between molecules, opening up a new realm of chemical behavior. The device is such that the speed of the molecules can be increased continuously, enabling the effect of energy on the process to be determined and the change-over to conventional behavior to be observed.