Anisotropy in the Simultaneous Excitation of Two Colliding Atoms to Various Substate Combinations. A Study of the Simultaneous Excitation of Both Collision Partners in He-He and He-Ne Collisions

摘要

In this thesis double-atom excitation (DAE) processes in atomic collision experiments are studied by measuring the angular correlation of two coincident photons emitted by both excited collision particles. The analytical expression for the angular correlation function is derived which contains as adjustable parameters the various (complex) excitation amplitudes integrated over all scattering angles. The He+He system is investigated, for projectile energies between 0.5 and 3.5 keV, in which both particles are excited simultaneously to the 2 sup 1 P state. The relation between photon correlations and atomic state correlations is investigated and the density matrix elements are calculated for a statistical distribution of the excited atomic substates into which a certain symmetry is incorporated. Collisions between metastable and groundstate He atoms are considered. Single-photon spectra are presented and compared with spectra from the He+He collision system. Coincidence measurements were performed on these collision systems to study possible double-atom excitations. Coincidences between two ultraviolet as well as an ultraviolet and a visible photon were measured. Also a measurement is reported of the relative population of the magnetic substates of the 3 sup 1 D state of helium. Coincidence measurements on two ultraviolet photons emitted upon Ne-Ne and He-Ne collisions are described and the double-atom excitations for these systems are studied. For Ne+Ne no coincidence peaks were found. For He+Ne double-atom excitation was observed and from the measured angular correlations the corresponding density matrix elements for some kinetic energies of the projectile. (ERA citation 12:042358)