The Structure and Properties of Weakly Bound Clusters
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Date
2020-10-07
Authors
Zhou, Ce
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
In this thesis, two novel methods are introduced to advance the study of gas phase clusters. The structure
similarity method is a computational technique that is able to quantify the structure difference for a pair
of isomers, with a structure interpolation technique capable of finding intermediates in-between the
isomer pair. A new experimental method, which couples differential mobility spectrometry with
ultraviolet photodissociation spectroscopy (DMS-UVPD), is also developed and tested. Three test cases
are discussed herein. These test cases showcase new theoretical techniques for mapping and visualizing
potential energy surface (PES) and finding transition state (TS) structures, as well as experimental
techniques of measuring UVPD spectra of DMS-MS isolated ion populations. Introduce of structure
similarity, a technique developed for unsupervised machine learning (ML), enables effective domain
of mapping PESs, which may subsequently be used to interpret experimental observations for systems
of high geometric complexity. The experimental DMS-UVPD technique is shown capable of isolating
ion species such that UVPD spectra may be recorded for characterization of analytes of interest. For
the test cases described herein, these new methods provide meaningful (sometimes anti-intuitive)
directions for future work.
For the structure similarity method, its PES mapping capability is tested in Chapter 3 with a collection
of protonated serine dimer cations, [Ser2 + H]+ to rationalize its infrared multiphoton dissociation
(IRMPD) spectrum. Eventually, the spectral carrier is assigned to a non-global minimum (GM) isomer
based on the partitioning information of the PES and spectral similarity. In Chapter 4, the
accompanying structural interpolation method is employed to find TSs that can rationalize a
regioselective alkylation reaction between a barbituric acid derivative and an alkyl-tricarbastannatrane
complex. By combining the interpolation method together with chemical intuition, a total of 3 reaction
channels are found, and the regioselectivity of the alkylation is identified as a kinetic effect. In Chapter
5, an acylhydrazone (AY) derivative, a photoswitch candidate, is examined using the DMS-UVPD
technique. Experimentally, the protonated [AY + H]+ cation is injected into the instrument for DMS
separation and laser interrogation, while theoretically, a number of neutral and protonated isomers are
sampled. Eventually, separation of the ion population is observed and attributed to some ion-solvent
cluster. Four isomers are found from theoretical calculation that may account for the UVPD spectra
Description
Keywords
serine dimer, tricarbastannatrane, acylhydrazone, DMS-UVPD, structure similarity, dissimilarity function, structure interpolation, tricarbastannatrane alkylation, gas phase clusters