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Electron and ion reactions with hexamethyldisiloxane and pentamethyldisiloxaneA mass spectrometry study of n-octane: Electron impact ionization and ion-molecule reactions A selected-ion-flow-drift-tube study of charge transfer processes between atomic, molecular, and dimer ion projectiles and polyatomic molecules ethane, propane, and n-butane Dissociative ionization of hexamethyldisiloxane ͑HMDSO͒ by electron impact is investigated using Fourier transform mass spectrometry. Absolute total and partial ionization cross sections are measured and the results compared with previous studies. The collision-induced dissociation technique is used to probe the fragmentation pathways of ions, providing insight into the production of neutral products from the electron impact ionization. Ion-molecule reactions of Ar + and HMDSO ions with the parent gas molecule are studied, and isotope studies are used to evaluate the possible reaction mechanisms.

A pulsed-leak valve that allows the introduction of a prolonged, flat, and controllable pulse of gas is described. Test results from the valve that utilized a Fourier transform ion cyclotron resonance mass spectrometer with Ar and C2H6 as the sample gases indicate that the valve functions as expected and yields basically rectangular pressure profiles in the cell region. The rise and fall times are similar to those of just the stand-alone pulsed valve and are believed to be determined mainly by the design of the vacuum system, rather than the design of the pulsed-leak valve. Kinetic data for the reaction of Nb(+) with C2H6, acquired with the use of the pulsed-leak valve to introduce the C2H6 gas, demonstrates the practical application of this valve for kinetic and other analogous studies. Use of the pulsed-leak valve greatly reduces the loss of the reactant ion signal during the cooling period.

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