<p> Calculations have been done for H₂O, F₂CO, Cℓ₂CO, H₂CS, F₂CS and Cℓ₂CS, to determine the transition energy and oscillator strength of the ¹A₂ ← ¹A₁(n → π*), ¹A₁ ← ¹A₁(π → π*), ¹B₂ ← ¹A₁(n → σ*) and ¹B₁ ← ¹A₁(σ → π*) transitions. Eigenvalues were obtained from CNDO programs and used to calculate the oscillator strength at three levels of approximation. </p> <p> The ¹A₁ ← ¹A₁(π → π*) transition of Cℓ₂CS has been analysed. Four ground state and three excited state frequencies were found. Coon's method was used to establish the assignment and predict an excited state bent out of plane by 26.6°. </p> <p> A previously unassigned transition in Cℓ₂CS has been labelled as A₂ ← ¹A₁(n → π*), on the basis of CNDO calculations, and five ground state frequencies have been found in the spectrum. </p> / Thesis / Master of Science (MSc)