Multi-dimensional Analysis of Molecular Clusters in the Gas-phase

Abstract

In this thesis, interactions and properties of novel gas-phase clusters are studied. These gas-phase clusters often possess unique geometries and unexpected properties, which are influenced by the forces and interactions between the moieties within the cluster. Spectroscopic methods and ion mobility methods are coupled with tandem mass spectrometry to elucidate the cluster properties and geometry. IRMPD provides insight toward the nature of the cluster by their IR fingerprints, which can be used in parallel with tandem mass spectrometry method such as CID to provide further information. In addition, ion mobility methods are used to differentiate conformational differences between isomeric clusters. In chapter 3, IRMPD and CID of deprotonated fluorinated propionic acids are studied. In analytical studies of short chain per- and polyfluoroalkyl substances (PFAS), the quantification and the identification of these carboxylic acids are done by monitoring the carbanion signal after the loss of CO2. The degree of fluorination influences fragmentation under IRMPD and CID, leading to fragmentation pathways such as formation of FCO2– and HF elimination. Fluorinated propionic acids with at least one fluorine atom bound to the terminal carbon yield FCO2–, whereas loss of HF is observed in polyfluorinated species with at least one fluorine bound to the α-carbon. The formation of FCO2– and HF elimination products occur through a four-membered ring transition state. Chapter 4 describes the study of aromatic organometallic compounds such as cyclopentadienyl that are known to form sandwich complexes with counter cations, because the dominant interactions between the cation and the anion are Coulombic interactions and ion-induced dipole interactions. This work focuses on studying the influence on the geometry of the cluster by reducing the symmetry of the aromatic compound through clustering 1,2,3–triazolide and 1,2,4–triazolide with various alkali metal cations (with an excess of one cation to preserve cationic states). Through a combination of IRMPD and DFT calculations, the primary interaction between the alkali metal cations and the triazolide is found to be dominantly ion-dipole interactions and lone-pair donation interactions. This results in the geometry of the 1,2,3–triazolide clusters to be a 3D compact structure, whereas the 1,2,4–triazolide analogues are found to be more open with longer distances between the cations. Potential overtone bands or combination bands associated with the C-H wagging motion and ring torsion motion are found between the 1500 – 1800 cm–1 region. Chapter 5 is a study on the clusters of perfluorinated dodecaborate cages, B12F122–, with protonated diaminoalkanes H2N(CH2)nH2N (n = 2 – 12) through a combination of IMRPD action spectroscopy and ion mobility spectrometry. I focus on characterizing the different singly-charged clusters of the form [B12F12 + H2N(CH2)nNH2 + H]– and doubly-charged clusters of the form [2(B12F12) + H2N(CH2)nH2N + 2H]2– (n = 2 – 12). Three unique geometries are found for the singly-charged clusters, a low energy proton-bound ring geometry where intramolecular hydrogen bonding occurs between the two amine functional groups, a bidentate geometry (where both amine groups bind to the B12F122– moiety), and a monodentate geometry. For the doubly-charged clusters, the doubly protonated diaminoalkane act as a tether between the B12F122– cages. The major fragmentation channels of the singly-charged and doubly-charged clusters are found to be: (i) proton-transfer leading to production of HB12F12– and (ii) the loss of B12F122–. Formation of HB12F12– likely leads to further gas-phase reactions that can yield compounds such as [B12F11 + N2]–. Travelling wave ion mobility spectrometry (TWIMS) analysis of HB12F12– finds CCSTWIMS = 142 ± 6.7 Å2. IRMPD spectroscopy, aided by computational modelling, indicates that the bidentate conformation is the major sub-population in the gas-phase ensemble.