Studies of ion molecule reactive processes, electron impact ionisation, and inelastic collisions in state selected molecular beams (1997)
AuthorsHarris, Sean Anthonyshow all
Alkali metal ion sources have been designed for the production of Li+, Na+ and K+ ion beams. The thermionic emission of alkali metal ions from heated synthetic zeolites is utilised to produce the alkali ions. As a precursor to crossed beam studies of the reactions of the alkali metal ions with spatially oriented symmetric top alkyl halides, the ion molecule chemistry of K⁺ with CH₃X and tertiary C₄H₉X where X= Cl or Br has been examined for collision energies up to 5 e V using a Drift Tube Mass Spectrometer. The electron impact ionisation cross sections for the inert gases, H₂, N₂, SF₆, CC1₃H and the molecules CH₃X where X= H, F, Cl, Br, I, have been measured. The ionisation efficiency curves for Ar, CH₄, CH₃F, CH₃Cl and CH₃Br from threshold up to 200 e V have been determined. The cross sections for the loss of hexapole focused upper Stark state molecules from ∣JKM〉 rotational state selected molecular beams of CH₃F, CH₃Cl and CF₃H have been measured. The upper Stark state molecules are defocused from the beam in rotationally inelastic collisions with a. scattering gas introduced to the hexapole. The long range attractive van der Waals interaction between the colliding species has been used to account for the magnitude of the cross sections from consideration of rotational transitions of the ∣JKM〉 state selected beam molecules where ∆M = ±1 or ∆J = ±1. The seeded beam technique has been used to determine the velocity dependence of the defocusing cross sections.