Venkatnarayan Ramanathan

Laser Induced Fluorescence Spectroscopy of Selected Organic Molecules in Supersonic Jet Expansion

The thesis is concerned with the gas phase electronic spectroscopy of selected aromatic molecules under the supersonic jet expansion environment. The main issues addressed in the work embodied in this thesis are conformational analysis and vibrational mode mixing in few selected organic molecules. Fluorescence excitation and dispersed fluorescence spectroscopy techniques have been employed with the help of tunable narrow spectral bandwidth UV lasers. Computational ab initio and DFT (density functional theory) methods have been extensively employed to support the experimental observation. In chapter K the theoretical principles underlying laser induced fluorescence, supersonic jet expansion and computational chemistry are detailed followed with a brief description about the methodology of the experiment and computation in the second chapter. Conformation of phenetole 2(p-fluorophenyl)ethanol have been determined where the former is shown to exist in a single conformer in the jet and three conformers of the latter are observed in the jet. Using computational methods, these observations are corroborated and details of these are given in parts A and B of chapter 3. In the same chapter, conformation of ephedrine and fluorescence studies of tryptamine and tryptophan are also detailed, fluorescence results show no difference from the earlier reports which pertained to ionization spectroscopy methods. These details are given in parts C and D of chapter 3.S1↔S0 electronic spectroscopy of 1-methoxynaphthalene, styrene and p-fluorostyrene(4FS) show extensive mode mixing characteristics which are detailed in chapters 4 and 5.The out-of-plane vibration of the vinyl group in styrene and 4FS get extensively mixed with several other ring vibration modes upon electronic excitation to the S1 electronic state.