Electronic spectroscopy of biological relevant species and their complexes with solvent molecules

Graduation date: 2005In this dissertation, I present electronic spectroscopy of a few biologically\ud relevant species and their complexes with solvent molecules in the gas phase using\ud a variety of techniques, including resonantly enhanced multiphoton ionization\ud (REMPI), laser induced fluorescence (LIF), and zero kinetic energy (ZEKE)\ud photoelectron spectroscopy. My work on several methylated uracils and thymines\ud and thymine-water complexes alludes to a new interpretation with regard to the\ud origin of the photostability of our genetic code. I believe that it is the water solvent\ud that stabilizes the photophysical and photochemical behavior of these bases under\ud UV irradiation. For systems that demonstrate vibrational resolution in the first\ud electronically excited state (S₁) and the cationic state, I performed vibrational\ud analysis of both states with the aid of ab initio and density functional calculations.\ud These observations are explained in terms of the structural changes from the\ud ground state to S₁ and further to the cation. To bridge results from the gas phase to\ud the solution phase, I also report studies of supersonically cooled water complexes\ud of the three isomers of aminobenzoic acid. Density functional theory calculations are carried out to identify structural minima of water complexes in the ground state.\ud The solvation mechanism is investigated based on vibrational analysis of the S₁\ud state of the neutral complex and the shift of ionization thresholds with increasing\ud water content