The determination of optical absorption intensities using the Xα scattered wave method

A density matrix formulation for optical absorption is developed within the Xα scattered wave theory using the transition state concept. Oscillator strengths for optical excitations in H+2, H2, and FeCl4−1 are given for the f (∇V) form. In H+2, oscillator strengths accurate to about 10% are found for R?2.0 a0 (the equilibrium nuclear separation). In H2, the intensity of the X 1Σg→B 1Σu transition at equilibrium is very accurately described (error ? 10%), but the X 1Σg→C 1Πu transition intensity is not satisfactory due to the diffuse character of the 1Πu state. The errors in the H2 and H+2 intensities are associated with specific defects in the scattered wave model. These defects should not, however, cause significant errors in many systems of chemical interest. Consistent with this viewpoint, semiquantitative agreement is found between the theoretical and experimental intensities in FeCl4−1.