Ab initio calculations of isomerization reaction of diphosphene 1-sulfide to thiadiphosphirane

Ab initio Calculations of the isomerization reaction of diphosphene 1-sulfide (2′) to thiadiphosphirane (3′) suggest that the energy barrier of the reaction in the ground state is 25 kcal/mol and that 2′ lies 21 kcal/mol above 3′, while the calculations show that there exists one local minimum on the lowest triplet energy surface.     

MO Study of the photochemical behavior of the imine bond

The photoisomerization of imine compounds is studied in terms of an ab initio MO CI calculation. The potential curves of the syn-anti isomerization via the rotation and the inversion are examined for benzaldimine. It is suggested that the photoisomerization is initiated through the rotation around the C? N bond in both singlet and triplet states. The ease of the photoisomerization is found to be determined by both the conformation of phenyl ring in the ground state and the energy difference of vertically excited states between two isomers.     

Precise pariser-parr-pople molecular orbital calculations using new-γ. A novel guiding principle for the design of functional materials

For precise Pariser-Parr-Pople molecular orbital (PPP MO) calculations, the values of the spectrochemical softness parameter k of a new two-center electron repulsion integral new-γ were evaluated based on an appropriate partial structure of polycyclic aromatic hydrocarbons (PAHs). The spectroactive aromatic sextet resonance system (ASRS) was defined as a spectroactive partial structure of a molecule. The calculated excitation energies of the p-band of PAHs accurately reproduced the observed ones.     

Electronic structure of transition-metal complexes. I. Parametrization for CNDO/2 method

A new parameterization for the first transition metal has been proposed in the framework of CNDO /2 method. We carried out CNDO /2 calculation of hexamine complexes [M(NH₃)₆]²⁺ and hexa-aquo complexes [M(OH₂)₆]²⁺ in the high spin state where M = Mn, Fe, Co, Ni, and Cu, using new parameters. It is shown that the calculated order of binding energy is Mn? L < Fe? L < Co? L < Ni? L ≈ Cu? L (where L means the ligand), and is in good agreement with experiment. We discussed how the orbital nodes affect the nature of bonding between metal and ligand.     

SCFMO calculations of heteroatomic systems with the variableβ approximation

The SCFMO method in the variable approximation has been extended to heteroatomic systems. The transition energies and bond lengths of a group of nitrogen- and oxygen-containing molecules have been calculated and the singlet transition energies are in good agreement with experiment.

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Zusammenfassung Die SCF MO Methode in der Näherung der variablen wurde auf Systeme mit Heteroatomen ausgedehnt. Die Übergangsenergien und Bindungslängen einer Gruppe von Molekülen mit Stickstoff- und Sauerstoffatomen wurden berechnet. Die Singulettübergaugsenergien befinden sich in guter Übereinstimmung mit dem Experiment.

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Résumé Nous avons étendu la méthode SCF MO dans l'approximation des variables aux systèmes hétéroatomiques et calculé les énergies de transition et les longueurs de liaison d'un groupe de molécules avec nitrogène et oxygène. Les énergies des transitions singulets s'accordent bien à l'expérience.

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Supported by the U. S. Atomic Energy Commission and National Science Foundation.     

An application of RPA theory to conjugated systems in the excited states

In order to obtain a relationship between the molecular dimension and the correlation effect, RPA method has been applied to the calculation of electronic transition energies of linear polyenes. It has been found that the effect of electron correlation on the excitation energy decreases with increasing the size of molecule. The calculated oscillator strengths are remarkably improved by RPA calculation.     

A theoretical study on the photodissociation of C3O2

The photodecomposition of C₃O₂ into C₂O and CO is studied with the ab initio MO calculation. It is found that, starting from the second excited state of C₃O₂ (_u), the ground-state C₂O (triplet) is yielded through the bent dissociation. The stable structure of the excited triplet state of C₃O₂ as an intermediate is also demonstrated.     

SCF calculations of aromatic hydrocarbons the variable β approximation

The transition energies and intensities of naphthalene, anthracene, phenanthrene, pyrene, and azulene are calculated with a variable modification of the Pariser-Parr-Pople method. In this procedure each is determined from the bond order after every iteration. The dependence of on bond order is given by = –0.51 p + A ₀ eV where A ₀ is –1.90 eV (naphthalene and azulene), –1.84 eV (anthracene and phenanthrene), and –1.82 eV (pyrene). Precise knowledge of the molecular geometry is not required and the results are in good agreement with experiment.

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Zusammenfassung Die elektronischen Anregungsenergien sowie die zugehörigen Intensitäten von Naphthalin, Anthrazen, Phenantren, Pyren und Azulen wurden mit der Modifikation der variablen der Pariser-Parr-Pople Methode berechnet, bei welcher die -Werte nach jedem Iterationsschritt als Funktion der Bindungsordnung neu berechnet werden. Ihre Abhängigkeit ist durch = –0,51 p + A ₀ eV gegeben, wobei A ₀ –1,90 (Naphthalin und Azulen), –1,84 (Anthrazen und Phenantren) bzw. –1,82 (Pyren) ist. Für das Verfahren ist die genaue Kenntnis der Geometrie des Moleküls nicht vonnöten und die Resultate befinden sich in guter Übereinstimmung mit dem Experiment.

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Résumé Nous avons calculé les énergies et intensités des transitions électroniques de naphthalène, Anthracène, phénanthrène, pyrène et azulène par une méthode PPP modifiée, où les sont déterminés des indices de liaison p après chaque itération: = –0,51 p + A ₀ eV, où A ₀ = –1,90 (pour naphthalène et azulène), –1,84 (anthracène et phénanthrène) et –1,82 (pyrène), respectivement. On n'a pas besoin des géometries exactes des molécules. Les résultats s'accordent bien à l'expérience.

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Supported by the U.S. Atomic Energy Commission and National Science Foundation.     

Electron interaction in molecules

An idea of electron interaction in molecule has been applied to the SCF MO calculations of theπ-electronic structure of some complex aromatic hydrocarbons and their derivatives. The theoretical results for singlet and triplet transition energies, first ionization potentials and bond lengths agree fairly well with the experimental data. A correlation equation between the valence state ionization potential and the one center electron repulsion integral has been proposed. It has been shown that the electron repulsion in molecule is considerably smaller than in free atom. The present calculation shows that we can treat sulphur as a normal heteroatom analogous to oxygen and nitrogen.     

Partial structure analysis of conjugated systems I

A new method for analysing the partial structure of conjugated systems is proposed. The present method is applied to the most important partial structure, benzene, which is closely related to aromaticity. The calculated results are in accord with the previously proposed indices of aromaticity.