<p>The near-ultraviolet vapour-phase absorption spectra of oxalyl fluoride, oxalyl chloride and oxalyl bromide have been investigated under low, medium and high resolution. Two discrete spectral systems have been observed for each of these molecules. The transitions responsible for the electronic spectra have been identified as singlet-singlet and singlet-triplet transitions associated with n ➛π * orbital electron promotion. The vibrational and rotational structures accompanying these transitions have been analyzed and are in general agreement with theoretical predictions. The molecules remain planar and trans in their excited states.</p> / Doctor of Philosophy (PhD)