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The use of the CNDO method in spectroscopy

VI. further n — π* transitions

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Abstract

The Pariser approximation for the two center Coulomb repulsion integrals Γ rshas been replaced by the Nishimoto-Mataga approximation in the original CNDO/S method. This modification has significantly improved the calculated position of the benzene 1 B 1u 1 A 1g(1 L a ) electronic transition in benzenoid compounds. The calculation of transition moments of n — π * transitions is also considered. These moments vanish formally in any theory employing the ZDO approximation since integrals of the form 〈2s¦er2p〉 vanish even when the 2s and 2p atomic orbitals are on the same center. In this work the ZDO approximation is abandoned in the evaluation of the electronic transition moment resulting in calculated intensities for n — π *, 1W←1A, transitions which are in good agreement with experiment.

Zusammenfassung

Die Näherung für die Zweizentrencoulombintegrale nach Pariser in der ursprünglichen Form des CNDO/S-Verfahrens wurde durch die von Nishimoto-Mataga ersetzt, wodurch sich der 1 B 1u1 A 1g(1 L a)-Übergang in benzoiden Verbindungen besser ergibt. Die n — π *-Übergangsmomente, die bei ZDO-Annahme immer verschwinden, weil dann 〈2s¦er¦2p〉 auch für an gleichen Zentren liegende Orbitale Null ist, werden hier berechnet, und zwar für den 1 W1 A-Übergang, wobei die Übereinstimmung mit dem Experiment befriedigend ausfällt.

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Supported in part by NSF Grant No. GP 15944.

Procter and Gamble Research 1969–70; Ethyl Corporation Research Fellow 1970–71.

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Ellis, R.L., Kuehnlenz, G. & Jaffé, H.H. The use of the CNDO method in spectroscopy. Theoret. Chim. Acta 26, 131–140 (1972). https://doi.org/10.1007/BF00526540

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  • DOI: https://doi.org/10.1007/BF00526540

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