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This Thesis reports the results of detailed isotopic studies carried out on three main groups of compounds, MMe2(M= Zn,Cd,Hg), MH 4(M= Si,Ge,Sn) and B(OMe)3 (Me&61 12CH 3,13CH3,12CD3). The infrared and Raman spectra of four isotopic species, 12CH 3, 13CH3, 12CD3, 13CD3, of dimethyl zinc, cadmium and mercury have been recorded, the fundamental frequencies corrected for Fermi resonance and anharmonicity and the empirical force field of each compound calculated. By incorporating interaction force constants determined by ab initio methods, semi-empirical force fields have also been calculated for these three compounds. A comparison of the scaled ab initio force fields with the empirical force field shows that properly constructed basis sets which employ effective core potentials are capable of producing results of similar quality to near Hartree-Fock calculations on molecules containing lighter atoms. The absolute infrared intensities in the 12CH3 isotopes of dimethylzinc, cadmium and mercury and in (12CD3)2Zn have been measured and the associated electrooptical parameters and atomic polar tensors calculated. The electrooptical models which appeared capable of explaining hydrocarbon infrared intensities have been shown to be invalid for these organometallic compounds. Atomic polar tensors have proved to be the more satisfactory means of representing infrared intensities generally. The absolute infrared intensities of SiH4, GeH4 and SnH4 have been remeasured in order to clarify the confusion over previous conflicting results. The unusual intensity patterns and the technological importance of these compounds in chemical vapour deposition made more precise intensity data desirable. The link between the gas phase intensities of these compounds and their gas-crystal shifts has been discussed and the electrooptical parameters and atomic polar tensors have been calculated for all three compounds. Three isotopes of trimethoxy boron; B(O12CH3)3, B(O13CH 3)3 and B(O12CD3)3 have been prepared and their infrared and Raman spectra recorded. The new 13C shifts allowed the spectra to be analysed in greater detail than was previously possible. A rudimentary force field of trimethoxy boron has also been calculated.

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The main focus of this work is using the infrared-infrared (IR-IR ) double resonance spectroscopic technique to study the 2³Πg, a³Σ⁺u triplet ground states, and the A¹Σ⁺u ~ b³Πu coupled states of the Rubidium dimer molecule. The initial analysis of the 2³Πg state involved separated analysis of the rotational and vibrational Bv and Gv functions to extract the molecular Dunham coefficients from the data. This was to avoid cross correlations between rotational and vibrational parameters because there was limited amount of rotational energy level data which included in addition perturbations between this state and other electronic states in the same region. An initial RKR potential energy curve was constructed based on this analysis. Subsequently this approach was augmented by a joint analysis of the 2³Πg state and the triplet ground state. This analysis was based on bound-free spectra, i.e. fluorescence from bound levels of the upper state to the continuum of the lower state. We present a comparison of these two approaches to the data analysis by testing the resulting potential energy functions through comparison of the calculated ro-vibrational energies against the observed energy level values The fluorescence from a discrete ro-vibrational level of the a bound upper state 2³Πg also includes transitions to discrete bound ro-vibrational levels of the triplet ground state (bound-bound emission). Accurate determination of the transition frequencies of the observed fluorescence spectroscopic lines allowed us to construct a reliable potential energy function that augmented our previous results on this state and corrected misinterpretation of that data in the literature. Similar infrared-infrared (IRIR) double resonance excitation of the 3¹Σ⁺g state was also used to observe resolved fluorescence spectra to the A~b states coupled by strong spin-orbit interaction. From the IRIR resolved fluorescence, we have filled the gap in the data range 12000cm-1 to 14000cm-1 of these coupled states for the Ω=0u⁺ component. / Physics

published_or_final_version / abstract / Chemistry / Master / Master of Philosophy