Electron-impact ionization of the SiCl3 radical

We describe improvements to the fast-beam apparatus that has been used extensively for electron-impact ionization cross section measurements for atoms, molecules, and free radicals in our group for the past 15 years. A high-intensity, dispenser-type electron emitter capable of producing an electron beam of more than 2 mA at electron energies above 50 eV is used instead of a conventional indirectly heated, oxide-coated electron source. We also replaced the channel electron multiplier by a position-sensitive, triple multi-channel plate ion detector. Experiments using well-established ionization cross sections in conjunction with extensive ion trajectory simulations were carried out to verify the performance of the modified fast-neutral-beam apparatus. This apparatus was subsequently employed in the measurement of absolute partial cross sections for the formation of various singly charged positive ions produced by electron impact on SiCl3 for impact energies from threshold to 200 eV. A comparison with calculations and with the previously reported ionization cross section for SiCl4, SiCl2, and SiCl is also made. (C) 2008 Elsevier B.V. All rights reserved.