Gasphasen-Chemie negativer Ionen des Tris(trifluormethyl)phosphans und Charakterisierung einer zylindrischen offenen ICR-Zelle mit Elektroden unterschiedlichen Durchmessers

Abstract

In a five sections cylindrical ion cyclotron resonance (ICR) cell the ion chemistry of tris(trifluoromethyl)phosphine has been investigated. The only major negative primary ion, produced by dissociative electron attachment is the phosphide ion (CF3)2P- , which reacts at elevated kinetic energy with the neutral molecules at 2x10-7 mbar to produce three phosphoranides: CF3PF3-, (CF3)2PF2-, and (CF3)3PF-. Simultaneously, three minor ions CF3-, F-, and C2F3- are formed by Self-Collision Induced Dissociation. Ion-molecule reactions between CF3- and the (CF3)3P has also been investigated. Positive ions form phosphonium ions and a diphosphonium product ion, (CF3)2P-P(CF3)3 , whereas no P-P bond is observed with negative ions. All the structures and reaction pathways have been investigated theoretically with the aid of DFT calculations. The results are in excellent agreement with the experiments.Several approaches have been implemented to study ion-ion interactions of singly charged positive and negative ions in a new open five sectional cylindrical ICR cell with an unusual geometry, capable to trap and detect both positive and negative ions in different axial regions simultaneously. Although single shot experiments, which were initially done in an attempt to achieve ion-ion interactions, did not lead to neutralisation of the reactant ions, therefore RF-pulse and pulse sequences with different shapes, frequencies and durations were implemented to establish longer axial overlaps between positive and negative ions in a shared central region. These RF-driven ion-ion spatial overlaps are discussed in detail in this article. Specific characteristic behaviours of the new ICR cell have been also studied.Single shot experiments were done in a new open cylindrical ICR cell to establish ion-ion collisions between positive and negative ions of SF6 in the gas phase for the first time. The role of pressure was illustrated to encourage high ion densities to be a prerequisite for ion-ion reactions. No electron transfer could be deduced from the experiments. Anion-Anion collisions could be indicated. The dynamics of applied potential changes on both ion polarities in a double well potential configuration were studied intensively. In depth analysis of radial excitation patterns of positive and negative ions trapped simultaneously in different stability regions reveals sharp discrimination in the extent of radial acceleration. SIMION simulations were done to probe several electric forces, which both positive and negative ions experience during radial excitation event. Axial component of radial dipolar excitation field was also analyzed. Distortion in radial ion trajectories during radial excitation event was indicated when both ion polarities were excited simultaneously.