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It is shown that CNDO S calculations provide 6 significant figures of accuracy in the energies of configurations, and 4 significant figures after configuration interaction. The pairing theorem is shown not to hold in the CNDO S method since all Fμν are calculated and since the Fμμ are not constant. It is further shown that the degeneracies required by the pairing theorem are not even approximated in naphthalene. Finally, using absorption and emission spectroscopic measurements, including triplet-triplet and excited singlet-singlet absorptions, the spectroscopic states of naphthalene are discussed in detail.

A method of using molecular symmetry in MO calculations is described. The method consists of determining the point group of the molecule, and establishing equivalence tables for atoms equivalent under various applicable symmetry operations. Ways of setting up symmetry orbitals are outlined. The determination of the symmetry species of molecular orbitals, of configurations and states of molecules are described.

He(I) and He(II) photoelectron spectra of some sulfinylamines are reported and assignments made on the basis of CNDO/S LCAO MO calculations. Insight into the effects of several substituents on the electronic structures of the compounds is obtained. The difference between the actual electronic structure of o , o ′, p -trimethyl sulfinylaniline and that interpolated from other molecules in the series is assumed to reflect a different conformation for this compound. The results of the MO calculations agree fairly well with the experimental data, although some discrepancies occur, concerning especially the π-donating capacity of a Cl substituent, and ionizations from chlorine lone pair orbitals.

The absorption spectra of azobenzene, of its m-bromo and p-ethoxy derivatives, of their conjugate acids and of benzalaniline are redetermined and carefully analyzed. Less precise data on the spectra of 9 other monosubstituted derivatives of azobenzene and their conjugate acids are reported. Energy level diagrams calculated by crude LCAO MO theory are used to interpret the observed transitions. The n → π 1 ∗ transition of azobenzene near 440 mμ may consist of two bands ascribed to the n a → π 1 ∗ , and n s → π 1 ∗ transitions. The 320-mμ band is the π 1 → π 1 ∗ transition, and the 230-mμ bands probably the φ → φ ∗ transitions. Buried in the asymmetric short wavelength side of the π 1 → π 1 ∗ transition are the transitions φ → π 1 ∗ . In the conjugate acids, the 420-mμ band is the π 1 → π 1 ∗ transition, the 235-mμ bands the φ → φ ∗ transitions, and the φ → π 1 ∗ transitions are again buried in the short wavelength side of the π 1 → π 1 ∗ transitions. The n a → π 1 ∗ transition is found at about 310 mμ at an intensity corresponding to the n → π ∗ transitions of the cis-free bases, thus confirming the previously postulated cis-conformation of the conjugate acids. The spectra of stilbene and of benzalaniline are reinterpreted in the light of the discussions. Substituent and solvent effects are discussed.