Electron-impact ionization of CCl4 and CCl2F2.

Absolute partial and total cross sections for electron-impact ionization of CCl4 and CCl2F2 are reported for electron energies from threshold to 1000 eV. The product ions are mass analyzed using a time-of-flight mass spectrometer and detected with a position-sensitive detector whose output demonstrates that all product ion species are collected with equal efficiency irrespective of their initial kinetic energies. Data are presented for production of CCl3(+), CCl2(+), CCl+, C+, Cl2(+), and CCl3(2+) from CCl4; and for production of CCl(2)F+, CClF2(+), CClF(+), (CCl+ + CF2(+)), Cl+, CF+, F+, and C+ from CCl2F2.

Low energy ion counting efficiency of a Johnston electron multiplier.

We report a measurement of the absolute efficiency of a Johnston Laboratories MMl electron multiplier for detection of 2-4 keV Ne(+). The measured detection efficiency depends both on ion impact energy and on the magnitude and direction of an externally applied electric field near the first dynode.