Revisiting the Renner–Teller Effect in the X ̃\u3csup\u3e2\u3c/sup\u3e\u3cem\u3eΠ\u3c/em\u3e State of CCN: Pulsed Discharge-supersonic Jet Single Vibronic Level Emission Spectroscopy

The CCN radical is a prototypical system for study of the Renner–Teller effect in its degenerate X ̃2Π ground state, with a number of experimental and theoretical studies carried out over the past 50 years. Most experimental studies have focused on the low-lying vibrational structure as observed in the high-resolution spectra of hot bands, or in emission. In this work, we have used pulsed-discharge supersonic-jet single vibronic level (SVL) emission spectroscopy from selected levels of the Ã2Δ state to probe the vibronic structure of X ̃2Π up to ∼6000 cm−1 above the vibrationless level. Around 50 levels were assigned, and these were fit to a Renner–Teller Hamiltonian to derive a detailed set of spectroscopic constants. Our data are compared with the results of recent high level coupled cluster calculations

MOLECULAR SPECTROSCOPY AND DYNAMICS OF REACTIVE CHEMICAL INTERMEDIATES STUDIED USING LASER INDUCED FLUORESCENCE (LIF), SINGLE VIBRONIC LEVEL (SVL) EMISSION AND RESONANCE ENHANCED MULTIPHOTON IONIZATION (REMPI) SPECTROMETRY.

ABSTRACT MOLECULAR SPECTROSCOPY AND DYNAMICS OF REACTIVE CHEMICAL INTERMEDIATES STUDIED USING LASER INDUCED FLUORESCENCE (LIF), SINGLE VIBRONIC LEVEL (SVL) EMISSION AND RESONANCE ENHANCED MULTIPHOTON IONIZATION (REMPI) SPECTROMETRY Lloyd Muzangwa, B.Sc. (Hons, Biochemistry). Marquette University, 2013 In the studies of complex chemical processes, it is necessary to postulate mechanisms involving transient intermediates such as radicals, ions, and pre-reactive complexes. The detection and characterization of these intermediates affords in ideal cases determination of the detailed chemical mechanism, which, in turn, can permit the development of rational strategies for removing undesired products and enhancing the yield of the desired species. This dissertation describes spectroscopic study of transient molecules and molecular complexes. Laser Induced Fluorescence (LIF), Single Vibronic Level (SVL) emission and Resonance Enhanced Multiple Photon Ionization (REMPI) spectroscopy has been used to probe the electronic states of NiI, NiBr, NiCl, CCN and chlorobenzene clusters (ClBz)n where n = 1-4. In this work, term energies and a complete set of vibrational parameters were derived for all the electronic states accessible for NiI, NiBr, NiCl and CCN. These vibrational parameters were compared to the recent high level ab initio calculations. REMPI spectra of chlorobenzene clusters formed in a He/Ar supersonic jet were obtained. Different types of non-covalent interactions (ð-ð stacking, CH/ð interactions, and halogen bonding) were found to be in operation in the ClBz clusters. To rationalize the experimental results, the clusters were characterized computationally using Density Functional Theory (DFT) and Time-Dependent DFT methods in combination with correlation consistent basis sets