Photostability of Gas Phase Ions: Mass Spectrometry, Laser Spectroscopy and Quantum Chemical Calculations

The fates of photoexcited molecules are difficult to predict owing to competition between several processes and relevant to this work includes photodissociation and electron photodetachment. The focus of this thesis includes investigating the action spectra of small ions (≤18 atoms) ranging from atmospherically relevant species to those that are fundamental aromatic chromophores. The measured adiabatic energies and photoproduct channels within this thesis provide important data for the benchmarking of quantum chemical calculations and guiding the design of photoactive molecules for application. Photodissociation action spectra spanning the 35000 – 43000 cm−1 (286 – 233 nm) range at both room-temperature and at 10 K for the isomers of protonated formylpyridine are reported. Product channels consistent with the loss of •H, H2, CO, •CHO, and CH2O are followed. The vibronic structure is assigned via Franck-Condon simulations, and with quantum chemical calculations, the adiabatic transition is assigned to a measured peak. For protonated 2-formylpyridine this was at 36560 ± 20 cm−1, 37430 ± 65 cm−1 for protonated 3-formylpyridine, and 36140 ± 15 cm−1 for protonated 4-formylpyridine. The SCS-CC2/aug-cc-pVTZ method predicted adiabatic energies within an average tolerance of 620 cm−1.