A Crossed-Beams Tandem Mass Spectrometer for Studies of Low Energy Ionic Collisions

摘要

The report describes the design, construction, and performance of the crossed-beams, longitudinal extraction, tandem mass spectrometer, LEICA. The function of LEICA is to measure total cross-sections for reactive ion-neutral processes at relatively low energies (around 100eV, to less than 1 eV, in the laboratory frame), and under conditions of high collision-energy resolution. Primary ions are velocity selected after mass analysis, and have a K.E. bandwidth of as small as plus or minus 0.1 eV. Target molecules are introduced as a modulated effusive beam, which intersects the beam of primary ions at 90 degrees. For reactive processes having favorable kinematics, this apparatus gives quite high K.E. resolution. As example, the reaction Ar(+) + D2 = ArD(+) + D was studied. The results of preliminary total cross-section measurements for the reaction H2(+) + H2O = H2O(+) + (undetected products) are presented. Several electronic circuits (which were designed and constructed specifically for LEICA, but which may be of general interest) are described.