<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)