THE LOWER EXCITED STATES OF SOME SIMPLE MOLECULES

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Abstract
The present and prospective rapidly increasing usefulness of good LCAO-MO calculations on the electronic states of simple molecules in the interpretation of observed excited states is pointed out. As examples, the observed and predicted states of, in particular, the π3π configurations of N2 and CO are compared with those of C2H2 and HCN and with those of CO2 and CS2. Further, the results of LCAO-SCF calculations on CO2 and on O3 are surveyed, and it is shown how these can be helpful in interpreting and understanding the ground and excited states of AB2 (expecially AO2) molecules in general. A new interpretation of the so-called d3П state of CO as a case b πu3πg, 3Δu state is proposed. Tentative interpretations of some of the ultraviolet absorption spectra of C2H2, HCN, and of a number of AB2 molecules are reviewed or suggested, including some discussion of the shapes of excited states. The AB2 discussion is a revision of one given earlier. Finally, following up a suggestion of Coon, it is pointed out that there exists strong evidence for slightly unequal A—O distances in certain excited states of C1O2 and SO2.