Electron Difraction Unit with Supersonic Molecular Beam and Cluster Beam

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Abstract
A supersonic molecular beam source was attached to an electron diffraction unit in order to study molecular structures and cluster structures. Because the density in a molecular beam is only a few times 1012 molecules per cm3, it was necessary to lower the pressure in the diffraction chamber to 5×10−8 Torr and to eliminate the back‐scattered electrons at large s values. This was accomplished by means of a very deep (45 mm) beam‐stop and a mask. Liquid helium cryopumping makes it possible to reduce the beam source bulkiness which, in turn, permits the placement of the scattering point as close as possible to the source (about 55 mm from the nozzle). Thus a target of the highest density is obtained, while a wide range of scattering is permitted. Reliable diffraction data have been obtained out to s = 45 Å−1. The main components of the diffraction unit are described, as is also the supersonic molecular beam source. A discussion is presented on the use of the apparatus.