The electronic structure and one-electron properties of BH computed from SCF and CI wave functions

The SCF and CI wave functions for BH, obtained in calculations described in detail elsewhere [2], are compared through their electron distributions and electron moments.Taken in part from a Ph.D. thesis submitted to the University of Toronto in 1971.     

SCF CI calculation of the electronic spectra of nitroso and nitro benzene

SCF calculation with CI has been found to give a reasonable value for the longest wavelength - ^* transition in nitroso and nitro benzene if a sufficient number of configurations are taken into considerations. The applicability of this method to the case of n- ^* transition is, however, of doubtful validity. For the electron density approximation of chemical reactivity simple Hückel calculation may be good enough if the parameters are carefully chosen.

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Zusammenfassung Eine SCF-CI-Berechnung ergab brauchbare Werte für die langwelligsten - ^*-Übergänge von Nitro- und Nitrosobenzol, wenn genügend Konfigurationen in die Rechnung einbezogen werden. Jedoch ist der Wert der Methode für die Berechnung von n- ^*-Übergängen zweifelhaft. Die Elektronendichte ist nicht wesentlich von der der Hückel-Theorie verschieden, so daß letztere für Fragen der chemischen Reaktivität ausreichend erscheint, wenn die Parameter sorgfältig gewählt werden.

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Résumé Un calcul SCF donne des énergies raisonnables pour les premières transitions - ^* de nitroso- et de nitrobenzène, quand on considère un nombre suffisant de configurations. Mais l'application de ce procédé aux transitions n- ^* est douteuse. Si l'on croisit soigneusement les paramètres, la méthode simple de Hückel semble suffir pour le calcul des densités électroniques dans des problèmes de réactivité chimique.

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Sincere thanks are due to Prof. P. 0. Löwdin, Uppsala, Sweden, for laboratory facilities, where a part of the work was done and to Mr Klaus Appel for Machine Computation on Alwac-III at Uppsala.     

Ab initio SCF and CI study of the electronic spectrum of pyridine N-oxide

Configuration interaction (CI) studies of ground, n *, * * electronically excited states are reported for pyridine N-oxide. The transition energy to the lowest * excited ¹ B ₂ state is calculated at 4.35 eV, compared to the experimental spectrum range of 3.67–4.0 eV. This state lies below the lowest n * excited ¹ A ₂ state calculated at 4.81 eV above the ground state. The only experimentally reported triplet state at 2.92 eV above the ground state is predicted to be the ³ A ₁ (*) state. The calculated energy lies at 3.27 eV. Numerous other high-lying singlet states as well as the triplet states have also been calculated. The intramolecular charge transfer character of the ground and the excited states have been studied in terms of the calculated dipole moment and other physical properties.     

SCF MO CI calculations on the electronic spectra of fluorenone and related compounds

The electronic spectra of fluorenone, 9-iminofluorene and 9-ethylidenefluorene are studied by means of the SCF MO CI calculation. It is shown that the lowest singlet-singlet transition of fluorenone located at 380 m. can be assigned to a - ^* transition (¹ B ₂¹ A ₁). The nature and location of the lowest triplet state are also discussed.

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Zusammenfassung Die Elektronenspektren von Fluorenon, 9-Iminofluoren und 9-Äthylidenfluoren werden mit Hilfe der SCF MO CI-Methode studiert. Es wird gezeigt, daß der niedrigste Sigulett-Singulett-Übergang in Fluorenon bei 380 m einem ^*-Übergang (¹ B ₂¹ A ₁) zugeordnet werden kann. Die Natur und Lage des niedrigsten Triplett-Übergangs werden ebenfalls studiert.

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Résumé Les spectres électroniques de la fluorenone, du 9 iminofluorène et du 9-éthylidène fluorène sont étudiés à l'aide de calculs SCF-MO-CI. On montre que la plus basse transition singuletsingulet de la fluorénone, située à 380 m, peut être attribuée à une transition ^* (¹ B ₂¹ A ₁ La nature et la position du plus bas état triplet sont aussi étudiées.

     

Electron spin resonance spectroscopy of the high- and low-spin dithiochelate manganese/II/ complexes

The ⁵⁵Mn hyperfine interaction has been analysed for MN/II/ complexes of the formula: I. Mn/dtch/₂ - high-spin, S=$\text{5}\text{2}$ II. Mn/dtch/2/NO//Cl/ - low-spin, S=$\text{1}\text{2}$, were dtch=dithiocarbamate, xanthate or thioxanthate ligand. The increasing π-acceptor properties of the ligands result in the decrease of isotropic hyperfine parameters K. This effect has been observed for both types of complexes. The axially symmetric hyperfine tensor depending on the π-properties of the ligands has been determined for the low-spin complexes. The spin polarization mechanism involving π-orbitals /xz,yz/ has been used for interpretation of the ¹⁴N superhyperfine tensor.     

SCF CI calculation of the electronic spectra of cis and trans isomers of stilbene and azo-benzene

SCF CI calculation has been made on cis and trans isomers of stilbene and azo-benzene. It has been shown that the electronic spectra of trans isomer should appear at a shorter wave length than the corresponding cis isomers, although the resonance theory reverses their positions. Experimentally azobenzene agrees with the conclusions of SCF theory while stilbene is better represented by the resonance theory.

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Zusammenfassung Für die cis- und trans-Isomeren des Stilbens und Azobenzols wird eine Berechnung nach der SCF-CI-Methode durchgeführt. Es wird gezeigt, daß die Elektronenspectren der Trans-Isomeren bei einer kürzeren Wellenlänge als diejenigen der cis-Isomeren liegen sollten, obwohl nach der Resonanztheorie eine umgekehrte Lage zu erwarten wäre. Die experimentellen Ergebnisse stehen beim Azobenzol in Einklang mit den Resultaten der SCF-Methode während sie beim Stilben besser im Rahmen der Resonanztheorie zu deuten sind.

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Résumé Nous avons calculé les spectres électroniques des isomères cis et trans du stilbéne et de l'azobenzène. Les spectres des isomères trans devraient apparaître à des longueurs d'onde plus courtes que ceux des cis correspondants. La théorie de résonance donne des résultats inverses. Les spectres des azobenzènes s'accordent aux conclusions de la théorie SCF, tandis que les stilbènes se représentent mieux par la théorie de résonance.

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Sincere thanks are due to Prof. P. O. Löwdin for providing financial assistance and laboratory facilities at Uppsala where a part of the work was done and to Dr. Klaus Appel for machine computation on Alwac III.     

SCF and CI Studies of Hund's rules for the effects of electronic correlation and delocalization. I

In connection with the reinterpretation of Hund's multiplicity rules for molecules, a detailed study has been made of the energy differences in the total energy and its components for the triplet and singlet Π_u states of the hydrogen molecule and the analogous states of the four- and six-membered hydrogen atom rings. For the hydrogen molecule, both SCF and CI studies indicated that the outer electron is considerably more contracted in the triplet than in the singlet state. In both approximations, the energy difference is dominated for all bond distances of chemical and physical significance by the electron-nuclear attraction component and not by the electron repulsion component as predicted by simple first-order perturbation theory. Although the correlation energy for each of the states is of the same magnitude as the energy differences considered here, the difference of the correlation energies is much smaller. It had little effect on the qualitative differences between these states of the hydrogen molecule. For the four- and six-membered rings, SCF studies were made on the lowest singlet and triplet states where one electron was promoted from the σ_g to a Π_u orbital. Even though the coupled electrons were more delocalized in these cases, the electron repulsion became relatively more important. However in all cases, the lower state had the highest electron repulsion energy and lower electron-nuclear attraction. The triplet state continued to have the more contracted outer open-shell orbital.     

An MNDO SCF MO investigation of the electronic structures and conformational preferences of model polycarbonate systems

Theoretical calculations within the MNDO SCF MO formalism have been carried out to investigate the relative heats of formation, conformation preferences and excitation energies of model polycarbonate systems. It is shown that the trans-trans and cis-trans configurations of diphenyl carbonate (DPC) are of comparable energy and have a strong energetic preference for orthogonal forms. The energy barrier for the interconversion of trans-trans and cis-trans orthogonal forms is small. Comparison of the electronic structure of DPC with simple carbonyl, carboxy ester and carbonate systems indicates that the nature of the first excited singlet of polycarbonate is of $\text{π → π}{}^1$ character in contrast to the $\text{n → π}{}^1$ assignment which has been described in the literature.     

Molecular structure,vibrational frequencies and ionization potential of tin dihalides: An ab initio SCF and CI study

The geometrical parameters for SnX₂ (X = Cl, Br, I) and SnX₂⁺ have been optimized at the SCF and Cl levels using non-empirical pseudopotentials and a basis set of double-zeta plus polarization quality. For the neutral molecules the geometrical parameters are in agreement with the experimental values, the difference being of only 2%. Vibrational frequencies and ionization potentials are also in agreement with experiment.     

Experimental and theoretical (INDO CI) electronic absorption spectroscopy in the examination of tautomeric phenomena in nitracrine and its nitre isomers

Electronic absorption spectroscopy was employed to examine tautomeric phenomena in N,N-dimethyl-N-(1-nitro-9-acridinyl)-1,3-propanediamine (known as nitracrine—WHO, or Ledakrin in Poland) which exhibits antitumour activity, and also to examine its three nitro isomers. The analysis of the experimental absorption spectra reveals that the compounds exist in the liquid-phase in at least two forms (most probably amino and imino tautomeric forms), remaining in an equilibrium which is strongly affected by the features of a solvent. This was qualitatively confirmed by examining frequencies and oscillator strengths of electronic transitions obtained for the lowest energy structures of a given form by two independent methods based on INDO approximation. The latter methods predict that the strongest transitions occurring below 280 nm have a π→π* origin, whereas the longest wavelength transitions may be either π→π* or n→π* type and cause a shift in electron density within the acridine aromatic system and attached nitro group and exocyclic nitrogen atom.     

A CNDO CI study of the electronic structure and spectrum of cyclopropane

The electronic states of cyclopropane were investigated using cndo ci calculations. Comparison was made between photoelectron spectra and computed ionization potentials. The structure of the ground state was investigated using localized molecular orbitals.     

An ab initio SCF + CI study of the SH3 and SF3 radicals

The symmetric sulfuranyl radicals SH₃ and SF₃ are studied by means of ab initio SCF + CI calculations. All geometries are optimized at the UHF level using analytical gradients. SH₃ is found to be a transition state corresponding to a hydrogen exchange reaction, whereas SF₃ is stable with respect to decomposition to SF₂ + F.     

SCF CI PPP study of the electronic structure of bromo derivatives of isomeric 1,5-, 1,6- and 4,6-benzo[h]naphthyridines

For six isomeric bromo 1,5-, 1,6- and 4,6-benzo[h]naphthyridines (bn) 1–6 and three dibromo derivatives 7–9, the electronic structure, wave number, oscillator strength values and dipole moments have been calculated by SCF CI PPP methods, also using the HMO approximation for comparison purposes. The calculated oscillator strength and wave number values were compared with the experimental data of ultraviolet spectroscopy; also comparison of the ultraviolet spectra of 1–9 with those of unsubstituted bn has been made. Plots of the calculated and observed wave number values of the investigated compounds show good correlation.     

On the Hartree-Fock approximation to the electronic structure of molecule in the intense radiation field and the strong vibronic coupling

The Hartree-Fock approximation has been generalized to incorporate the nonadiabatic effect of molecular vibration previously by Tachibana et al. Here, we will derive the Hartree-Fock equation which reflects also the nonlinear effect of the infrared radiation field as well by using the Bloch-Nordsieck transformation which was discussed first by Nguyen-Dang and Bandrauk in the field of molecular physics. The Hartree-Fock equation reflects the non-adiabatic coupling between an electron and a molecular vibration and between the electron and a infrared radiation fields. The infrared radiation field also affects the dynamics of nuclear motion.Dedicated to Professor J. Koutecký on the occasion of his 65th birthday     

CI AM1 study of the electronic structure of isomeric formyl benzonaphthyridines

For six isomeric formyl derivatives of 1,5-, 1,6- and 4,6-benzonaphthyridines the electronic structure and UV spectral values have been calculated by CI AM1 method. Correlations of the calculated and observed wave number values of considered compounds show good compatibility.     

An SCF and CI study of the properties of the HCl and CI2 molecules

The one-electron properties and polarizabilities of the HCl and Cl₂ molecules have been calculated using both SCF and CI wavefunctions. Agreement with experimental data, where such data exist, is found to be very good.     

A theoretical CNDO CI study of the electronic spectrum and structure of a spiropyran

The electronic structure and spectrum of a model compound of a spiropyran were investigated using an all valence-electrons CNDO CI method. The π → π^* electronic excitations are localized on a given half of the molecule. The photochromic process is discussed on the basis of charge densities and bond orders.     

Pseudopotential SCF and Cl investigation of the electronic structure of PdH,PdC and PdCO

The electronic structure of PdH, PdC and PdCO molecules has been investigated by means of pseudopotential multireference double-excitations configuration interaction method (PP MRD Cl). Three different optimized AO basis sets have been adopted for determination of bond lengths, dissociation energies, dipole moments and population analysis. The basis set optimized for the Pd³D)rd⁹5s¹) excited state is more suitable for describing the electronic redistribution occurring on Pd during formation of the band than that derived from the ¹S(4d¹⁰) ground state. Differences in the bonds of PdH, PdC and PdCO can be explained with these calculations. Correlation effects are crucial for understanding the chemical bonding.