Spectroscopic interrogation of differential mobility spectrometry selected, isolated, gas-phase molecular clusters

Abstract

One of the most elusive challenges facing mass spectrometry-based methods is the study of isomers. Oftentimes, isomers produce identical fragmentation spectra that make structural elucidation and assignment from MS data alone difficult. In this thesis, the problem of studying isomers is addressed by employing differential mobility spectrometry-mass spectrometry experiments coupled with ultraviolet photodissociation action spectroscopy (DMS-MS-UVPD). Using a combination of experimental and computational techniques, the validity of DMS-MS-UVPD studies for applications in isomer separation and distinction is verified. During the course of two subprojects, DMS-MS-UVPD is successfully applied to separate and distinguish between geometric isomers and tautomers. First, DMS-MS experiments are conducted, and the dynamic clustering behaviour of each species is determined. Once the clustering behaviour is well-characterized, the DMS-MS parameters are optimized to select for the species of interest and used as an ion filter for subsequent UVPD action spectroscopy experiments. The results from the action spectroscopy studies produce a vibronic spectrum that can be compared to theoretical models for correct isomer assignment. Due to the complexity of excited state phenomena, many computational models were used to accurately predict vibronic spectra, including Franck-Condon based approaches and non-adiabatic dynamics. The work presented in this thesis provides the framework for the use of DMS-MS-UVPD in other isomer systems.