The ¹A₂ ← ¹A₁ (π* ← n) electronic absorption spectrum of thioformaldehyde vapour has been investigated. The six excited state fundamental frequencies for both CH₂S and CD₂S are determined from the vibrational analysis. The three rotation constants and three symmetric top distortion constants for the 0⁰₀, 4¹₀ and 3¹₀4³₀ bands of CH₂S and the 0⁰₀, 4¹₀ and 5¹₀ bands of CD2S are determined from a least squares rotational analysis of these bands. The rotational constants of the 0⁰₀ and 4¹₀ bands of CH₂S and CD₂S are used to determine the structure of the molecule in the excited state. / Thesis / Doctor of Philosophy (PhD)

<p> The results of an investigation of the electronic absorption spectrum of carbon diselenide are presented. The synthesis of the compound from individual isotopes of selenium is described.. Some new observations and results from a reinvestigation of the infrared and Raman spectra are reported. The electronic absorption spectra of individual isotopic molecules were recorded and a detailed vibrational analysis of one of the observed systems in the spectrum has been made o The rotational structure of bands in this system has been examined. A preliminary study of two other systems are discussed. The spectra of carbon diselenide and the analogous carbon disulphide are compared and the similarity between the two spectra is shown. </p> / Thesis / Doctor of Philosophy (PhD)