Absolute differential cross-sections for keV energy ion and atom collisions with oxygen atoms
Hakes, Charles Lynn
Stebbings, R. F.
Doctor of Philosophy
Oxygen atoms are the most abundant constituent in the Earth's atmosphere between 200km and 600km, and thus are the most probable targets for precipitating ions and atoms at these altitudes. Differential cross sections for collisions involving oxygen atoms supply information necessary for numerically modeling the conditions in the Earth's upper atmosphere. Absolute cross sections, differential in angle, for electron capture by 500, 1500, and 5000eV protons in collisions with oxygen atoms are presented. The target, a mixture of atomic and molecular oxygen produced in a microwave discharge, is confined to a very short ($<$1mm) teflon-coated cell. The abundance of atomic and molecular oxygen in the target is determined using an electron-impact-ionization time-of-flight-mass spectrometer. The mass spectrometer signal, yielding the atomic oxygen density in the target cell, is calibrated by comparing the direct scattering of He(500eV) + O to the direct scattering of O(2000eV) + He. The charge transfer cross sections are integrated and compared to total cross sections reported in the literature.