Oscillator strengths in alternant hydrocarbons

The evaluation of oscillator strengths via the gradient operator is less uniformly successful than earlier calculations suggest. The inclusion of complete CI does not lead to a good agreement between calculated and observed f-values. It is shown that the failure of pi-electron MO-methods in predicting f should be attributed partly to the deficiencies of the simpler MO-models, and partly to the neglect of the polarisation of the sigma-electrons.