Drift Tube-Mass Spectrometer for Studies of Low-Energy Ion-Molecule Reactions

Apparatus has been developed for the mass spectrographic study of ion-molecule reactions occurring under gas-kinetic conditions. Ions are produced by electron bombardment inside a long drift tube containing gas at a pressure of up to about 0.7 torr. The ions diffuse down the drift tube under the influence of a weak electric field. A sample of the ion population at the end of the drift tube is extracted through a two-stage, field-free differential pumping section and passed into a 60° magnetic deflection mass spectrometer. The number of ion-molecule collisions in the drift tube may be varied over a wide range by changing the source position and/or the gas pressure. Information concerning the nature and probability of the reactions occurring is revealed by the resulting changes in the ionic mass spectrum.