A HYBRID DOUBLE-FOCUSING MASS-SPECTROMETER - HIGH-PRESSURE DRIFT REACTION CELL TO STUDY THERMAL-ENERGY REACTIONS OF MASS-SELECTED IONS

A new instrument is described that couples a reverse-geometry mass spectrometer operating at 5 kV to a high-pressure, temperature-variable drift reactor that operates at thermal energies. The first-stage mass spectrometer is a home-built instrument with the same dimensions and ion optics as a V.G. Instruments ZAB-2F. Ions exiting this instrument are decelerated to between 0 and 10 eV and focused on the entrance hole of the drift cell. The drift cell is 4.0 cm long and 1.52 cm in diameter and has a uniform drift field provided by stepped voltages applied to eight field guard rings. Pressure in the cell can be varied from 0 to 2 torr, and temperatures from 100 to 500 K. Ions exiting the cell are accelerated, passed through a quadrupole mass filter, and detected by an electron multiplier. A description is given of the ion optics used to focus and decelerate the beam from the first-stage mass spectrometer. Substantial analysis and discussion are given to ion energies in the cell and methods of pressure measurement. Experimental results obtained compare well with data in the literature when available. A new result on mobilities of Co+ ions in helium is presented. The data indicate that ions are present in both the ground state and metastable excited electronic state, exhibiting substantially different mobilities. © 1990 American Society for Mass Spectrometry.