Helium Atomic Beam Scattering from Clean (001) Surfaces of NaF.

摘要

Several improvements were developed for the atomic beam apparatus, including stabilization of the inlet temperature, cooling of the sample and the titanium sublimator, methods of precise alignment, and more accurate measurement of the beam angles. Measurements were made on the selective adsorption energy levels of He on NaF. Three levels were determined with good accuracy and a fourth one was also roughly determined. From these, a well depth of 7.5 meV and a Van der Waals constant, C(3) = 140 MeV - A squared, can be estimated. Measurements of intensities of diffracted beams were also carried out, and the two new phenomena recently predicted on theoretical grounds were found. These are the occurrence of intensity maxima due to multiple transitions (incident to absorbed to diffracted states), and the splitting of degeneracies in the energy levels due to perturbations by the periodic potential. Both of these effects provide new approaches to the determination of the potential parameters. (Author)