The near ultraviolet absorption spectra of cyclohexanone, cyclohexanone α, α, α', α'd₄ and cyclohexanone d₁₀ have been recorded and analysed under low and high resolution. The vibrational and rotational structure accompanying the electronic singlet-singlet ṉ→π* transition have been analysed. Some complementary information has been obtained from the infrared vapour spectrum of cyclohexanones. The geometries of the ground and first excited state have been determined. In the excited state configuration, the oxygen atom was bent out of the plane of the three adjacent carbon atoms by about 30º, and the carbon oxygen bond increases by 0.08 Å between the ground state and the excited state. Some ring modes are strongly active in the electronic spectra of the three isomers. This may indicate some coupling between the carbonyl group and the ring. The results obtained by band contour analysis are consistent with those obtained by calculation of a double minimum potential function, as well as those obtained in previous work on related molecules. / Thesis / Master of Science (MSc)