Investigation of atomic oxygen in mass spectrometer ion sources

Abstract

An atomic oxygen beam generated on a heated tungsten ribbon is used to simulate upper atmospheric mass spectrometer measurements. The neutral beam has a high purity of atomic oxygen and a very small angle dispersion. Different materials placed as inserts into the mass spectrometer ion source are exposed to atomic oxygen and the results are compared with exposure to molecular nitrogen under the same conditions. A movable flag in front of the ion source allows the separation of direct and reflected particles. Carbon dioxide is the major surface reaction product when each insert is first exposed to atomic oxygen. As the available carbon on the surface is depleted recombination into molecular oxygen starts and the carbon dioxide level falls. The observed loss is about equal on Nichrome V and gold, but is much less on aluminum.