CONSTRUCTION AND APPLICATION OF A DRIFT TUBE MASS SPECTROMETER FOR EXPERIMENTAL ION STUDIES

Abstract

A drift tube mass spectometer suitable for experimental ion studies was constructed. It contains the following features which yield improved performance over previous devices. The drift tube pressure is continually monitored and regulated by a control system which utilizes a servo-controlled valve to maintain a preset pressure with less than 1% fluctuation. The ion optics which incorporates retarding potential difference grids and the quadrupole mass analyzer have wider apertures so as to collect larger numbers of ions. A novel obstacle in the drift tube and a 93° ion deflector prevent virtually all UV photons and metastable species from producing background noise in the ion counting system. The data are stored on a multichannel analyzer by an automated data collection system which adds numerous data collection cycles together in order to produce curves with low levels of statistical fluctuations and high energy resolution. He+ ions in helium, Ne+ ions in neon and Ar+ ions in argon were studied with this apparatus. Measurements of the energy distribution functions of ions moving parallel or nearly parallel to the drift tube electric field were obtained at values of E/n ranging from 60 to 320 Td at 298±2 K. The results showed functions which were strongly asymmetrical about a single peak, structureless and differing significantly from a Maxwellian energy distribution function. The degree of asymmetry increased with increasing E/n for all degrees of enhancement three types of the high X of Ions. Various energy tail were evident. The mean energies of the functions were in all cases greater than the values predicted by the equation of wannier (1951, 1953). This was expected on theoretical grounds due to the nature of the experiment. Also, the trend of the amount of the variation as a function of E/n was consistent with the predictions of the theoretical analysis. The results of the measurements made with this system provide sufficiently accurate sets of data against which predictions of theoretical calculations and Monte Carlo simulations can be tested.