Low energy collisions of molecular ions with hydrogen, methane, and freon.

摘要

Measurements of total cross sections for collision induced dissociation (CID), proton abstraction, and charge transfer have been made for the reactants H+3+H 2, He, and Ar CH+4+CD 4,H2 , and Ar, and CF+3 F++CF4,H2 and Ar for laboratory collision energies ranging from a few to 400 eV. Isotopic substitutions of the target and projectile have been made where possible to investigate any isotope effects, and in some cases to more clearly identify product ions. The purpose of this investigation is to expand the limited database of collisional processes pertinent to hydrogen, methane, and Freon discharges and their numerical modeling.;Cross sections for CID are observed to be relatively constant and CID is an important process over the energy range studied for the methane and Freon experiments. Cross sections for proton abstraction are, for the most part small ( ≤ 10 A2), and this process is important only at the lowest collision energies. The newly formed ion produced from proton abstraction for all reactants studied often has sufficient internal energy such that it may autodissociate. Charge transfer is observed for higher impact energies and cross sections for this reaction do not exceed 15 A 2. In general, production of secondary ions is observed at or near the energetic thresholds required for ground state reactants. The role of internal energy contained in the primary ion beam and its effects on the measured cross sections presented here will be addressed.;In addition to total cross sections, kinetic energy distributions have been measured for H+, H2+, and H 3+ ions present in a low pressure hydrogen discharge. These measured ion energy distributions are compared to predicted values made by a recently developed Monte Carlo simulation which necessarily incorporates the cross section measurements presented here for the H3 + + H2 system, among others. Complete agreement between theory and experiment is achieved only if measured cross sections for select CID reaction channels are arbitrarily increased by a factor of 2--3. Possible justifications for this modification, in addition to other inadequacies and further improvements that should be made to this numerical model are elaborated on. The importance and implications of all the measurements presented in this work to hydrogen, methane, and Freon discharge modeling and the yet to be realized goal of complete characterization of a molecular discharge will also be discussed.