Akira Sadô

Electronic States of p‐Benzoquinone. VI. Molecular Geometry in the Excited Electronic State of the 4500‐A Absorption System as Derived from the Franck‐Condon Principle

The method used for evaluating the Condon overlap integral associated with any vibronic band of an electronic absorption system of an XY2 molecule, as developed by J. B. Coon and his co‐workers, is applied to more complex molecules. Thus, some information about the geometry of the excited electronic state of a complex molecule may be determined if the geometry in the ground state, the intensities of vibronic bands of the associated electronic absorption system, and normal coordinates and frequencies in both electronic states are known. The method is applied to the 4500‐A absorption system of p‐benzoquinone. Since the normal coordinate treatment for this molecule is only qualitatively valid, especially in its excited state, the results are expected to be more or less qualitative. If we take the resulting change of bond angles into account, the ring‐bending frequency of species Au in the excited electronic state is calculated to be 438 cm—1 by the method described in Part III of this series [T. Anno and A. ...

Electronic States of p‐Benzoquinone. V. Vibrational Analysis of the Vapor Absorption Spectrum around 4500‐A Region

The absorption spectrum of p‐benzoquinone vapor in the region between 4080 and 5100 A was photographed and measured. Although the theoretical calculation as well as the experimental crystal spectrum indicate that two singlet‐singlet electronic transitions exist in this region, prominent vibrational structure of the vapor spectrum can be interpreted as caused by a single forbidden electronic transition. If we assume that the hydrogen vibrations are not effective as perturbing vibrations which make the forbidden electronic transitions allowed through the vibrational‐electronic interaction, this fact suggests the following two sets of assignments for the symmetries of the forbidden transition and the perturbing allowed transition: (1) the spectrum is a superposition of 1Au, 1B2u←1Ag transitions perturbed by a 1B2u←1Ag transition, (2) the spectrum is caused by a single 1B1g←1Ag transition being allowed through vibrational‐electronic interaction with the allowed 1B1u←1Ag transition. Vibrational structure alone...

Semiempirical calculation on the electronic structure of the nitrogen-containing heterocyclic molecules. II. Electronic structure of pyrazine with particular reference to its n-π transition

The semiempirical theory of n—π and π—π spectra of nitrogen analogs of aromatic hydrocarbons proposed in Part I is applied to calculate the lower excited levels of the pyrazine molecule. The doubly excited configurations as well as singly excited configurations are considered in CI calculation. It is shown that the usual assumption of sp2 hybridization of the nonbonding orbital of the nitrogen atoms in the pyrazine molecule results in a considerably higher calculated value for the n—π transition energy as compared with experiment, even if the doubly excited configurations are considered. In order to bring the calculated values of the lowest 1Ag→1B1u,1B3g (n−π) transition energies in agreement with the observed values, the s character of the nonbonding orbital of the nitrogen atom should be taken as 0.103. Discussions which support the lower s character of the nonbonding orbitals of the nitrogen atoms in this molecule are presented.