Date of Award
Fall 2014
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
First Advisor
Reid, Scott
Second Advisor
Steinmetz, Raymond A.
Third Advisor
Timerghazin, Qadir
Abstract
Non-covalent interactions in halobenzenes (PhX) (X=F, Cl, Br) and phenylamine (C6 H5 NH2 ) have been studied here using resonance two-photon ionization (R2PI) spectroscopy combined with a linear TOF-mass spectrometer. Their interaction with polar molecules in form of ammonia (NH 3 ) and trifluorohalomethanes (CF3 X) has also been studied. DFT and TD-DFT calculations using M06-2X functionals were carried out on different cluster conformations to compliment experimental results. A general trend of broadness in homogenous dimers (PhX)2 , has been attributed to mainly the presence of multiple cluster isomers and Frank-Condon activity in the low frequency intermolecular vibrational modes. The van der Waals interactions between PhX and ammonia were all assigned to an in-plane σ-type geometry as compared to an out of plane π-type conformation. Stable halogen bonded dimer structures in the C 6 H5 NH2 ...CF 3 X system were also optimized. In the second part of this dissertation, a global analysis of spin-orbit coupling in the mono-halocarbenes, CH(D)X, where X = Cl, Br, I is presented. Mono-halocarbenes are model systems for examining carbene singlet-triplet energy gaps and spin-orbit coupling. Experiments probing the ground vibrational levels in these carbenes have clearly demonstrated the presence of perturbations involving a low-lying triplet. To model these interactions more globally, a diabatic treatment of the spin-orbit coupling is adopted, where matrix elements are written in terms of a purely electronic spin-orbit matrix element which is independent of nuclear coordinates, and an integral representing the overlap of the singlet and triplet vibrational wavefunctions. In this way, the structures, harmonic frequencies, and normal mode displacements from ab initio and DFT calculations were used to calculate the vibrational overlaps of the singlet and triplet state levels, incorporating the full effects of Duschinsky mixing. These results were then incorporated with the electronic spin-orbit matrix element into a matrix diagonalization routine that calculated the term energies of the mixed singlet-triplet levels, which were iteratively fit to the extensive experimental results from SVL emission and SEP spectroscopy for the halocarbenes. These calculations have allowed many new assignments to be made, particularly for CHI, and provided spin-orbit coupling matrix elements and improved values for the singlet-triplet gaps.