An Improved Drift Tube Mass Spectrometry

Abstract

Detailed descriptions of the drift tube technique of Kaneko-Megill-Hasted and a newly constructed apparatus are given. The apparatus consists of two sector type mass analyzers and a drift tube. Mass-identified primary ions are injected into the drift tube and thermalized by collisions with gasmolecules in the tube. After drifting through the tube, population of ions at the end of the tube is sampled with the second mass analyzer. The drift velocity of ions is measured by gate pulse technique the ionic mobility is determined. The average kinetic energy of drifting ions is calculated by Wannier's formula using the drift velocity measured experimentally. The cross section of reaction is calculated from the peak height ratio in the second mass spectra. By the use of buffer gas to dilute reactant gas, study of reactions having ordinary size of cross section, which would have dissipatall the primary ions if the reactant gas was not diluted, has become possible. Usually He gas is as buffer gas. Two mass analyzers are nearly the same. Each one has the radius of10cm. Whole apparatus differentially pumped so that the gas pressure in the drift tube can be increased as high as 1.8 The effective length of the drift tube is 8.4cm. The apparatus can cover the energy range from 0.044 eV(-330°K)to several eV. Reliability test of the apparatus has been made for both mobility measurement and cross section measurement.