Showing papers in "Theoretical Chemistry Accounts in 1965"
TL;DR: In this article, Valence Orbital Ionization Potentials (VOIPs) for the elements H through Kr in various configurations and for many states of ionization were reported, for the lighter elements the isoelectronic series were fitted to a quadratic equation, VOIP (q)=Aq2 + Bq+C.
Abstract: Average Energy of Configuration. Valence Orbital Ionization Potentials (VOIPs) are reported for the elements H through Kr in various configurations and for many states of ionization. For the lighter elements the isoelectronic series are fitted to a quadratic equation, VOIP (q)=Aq
2 + Bq+C. The significance of the A, B, and C parameters is discussed.
298 citations
TL;DR: In this paper, the transition energies and intensities of naphthalene, anthracene, phenanthrene, pyrene, and azulene are calculated with a variable β modification of the Pariser-Parr-Pople method.
Abstract: The transition energies and intensities of naphthalene, anthracene, phenanthrene, pyrene, and azulene are calculated with a variable β modification of the Pariser-Parr-Pople method. In this procedure each β is determined from the bond order after every iteration. The dependence of β on bond order is given by β = −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.
156 citations
TL;DR: In this paper, the vacuum ultraviolet absorption spectra of styrene, benzaldehyde, acetophenone and benzonitrile have been measured in the wavelength region of 1500 to 2200 A.
Abstract: The vacuum ultraviolet absorption spectra of styrene, benzaldehyde, acetophenone and benzonitrile have been measured in the wavelength region of 1500 to 2200 A. The absorption bands in the vacuum ultraviolet region appear at 200, 196, 189, 180 and 163 mμ for styrene; at 195,186, 178 and 165 mμ for benzaldehyde; at 196, 191, 179 and 167 mμ for acetophenone; at 187.5, 180 and 167 mμ for benzonitrile. Theoretical studies of π-electron structures have been carried out with styrene, benzal-dehyde and acetophenone by considering configurational interactions among the ground, locally excited, and charge-transfer configurations. The calculated transition energies and oscillator strengths are in good agreement with the observed values. The theoretical results show that the contribution of the charge-transfer configuration amounts to 58 and 68% in the excited states of the 238 mμ band of styrene and of the 232 mμ band of benzaldehyde respectively. This means that these two bands may be regarded as the intramolecular charge-transfer band. The electron affinity of the C=C and C=O groups were determined to be respectively −0.84 and −1.20 eV from the present analysis of the ultraviolet spectra.
70 citations
TL;DR: In this paper, weitgehende theoretische Interpretation der Spektren des Mono-aminobenzochinons-(1,4), des 2,5-Diaminobenochinon-(1.4) and des 1,5DiamINaphthochinions-(2,6), die Molekuldiagramme belegen deren Quadrupolcharakter.
Abstract: Im Rahmen einer durch die Heteroatom-Integrale nach Rasch und Resonanzintegrale zwischen nichtbenachbarten Atomen vervollstandigten LCAO-MO-Methode werden zunachst langwelligste Elektronenubergange und Molekuldiagramme fur Oxonol- und Merocyanin-Ketten berechnet und mit experimentellen Daten verglichen. Unter dem Aspekt der Kopplung von Merocyaninen gelingt dann eine weitgehende theoretische Interpretation der Spektren des Mono-aminobenzochinons-(1,4), des 2,5-Diaminobenzochinons-(1,4) und des 1,5-Diaminonaphthochinons-(2,6), die Molekuldiagramme belegen deren Quadrupolcharakter. In gleicher Weise wird die Absorption des Indigo und weiterer indigoider Farbstoffe diskutiert und neue Ergebnisse uber deren chromophore Systeme erhalten. Die charakteristischen indigoiden Eigenschaften werden aus dem Modell abgeleitet.
53 citations
TL;DR: In this article, the s-p content in cyclopropane, spiropentane, nortricyclene and 1,1 -dimethyl cyclopsropane was found to be sensitive to changes in the interorbital angle.
Abstract: The hybridization in cyclopropane, spiropentane, nortricyclene and 1,1 -dimethyl cyclopropane is calculated applying the criterion of maximum overlap. The s-p content in the general hybrids is found to be sensitive to changes in the interorbital angle Θ
ij. The results give information about the strain associated with bent bonds and its delocalization. The application also allows calculations of skeletal angles, such as ∢ C1 C2 C3 in nortricyclene, which determine the geometry of the molecule.
50 citations
TL;DR: In this paper, the semi-empirical treatment due to Pariser and Parr and to Pople has been used to calculate transition energies and intensities of the π−π* bands in the electronic spectra of 31 azines (aza-benzenes and aza-naphthalenes).
Abstract: The semiempirical treatment due to Pariser and Parr and to Pople has been used to calculate transition energies and intensities of the π−π* bands in the electronic spectra of 31 azines (aza-benzenes and aza-naphthalenes). A comparison with experimental data and a discussion of the wave functions for the ground and excited states are presented.
48 citations
47 citations
TL;DR: In this paper, the complete CI method was used to calculate the singlet energy levels of benzene molecule using π-electron approximation for two sets of semi-empirical parameters.
Abstract: Singlet energy levels of benzene molecule were calculated using the complete CI method in π-electron approximation for two sets of semiempirical parameters. The inclusion of triply-,tetra-, and hexa-excited configurations has practically no effect on the values of singlet energy levels as far as parametrizations which are common in semiempirical procedures are employed. On the other hand, using parameters which are very similar to those obtained with theoretically calculated molecular integrals, appreciable changes in the energy spectrum are observed.
45 citations
TL;DR: In this paper, the authors evaluate constantes de couplage hyperfin electron-noyaux a partir des fonctions d'ondes moleculaires and discutee sur l'exemple des radicaux libres nitroxydes.
Abstract: L'evaluation des constantes de couplage hyperfin electron-noyaux a partir des fonctions d'ondes moleculaires est discutee sur l'exemple des radicaux libres nitroxydes.
44 citations
TL;DR: In this paper, the antisymmetrized product of strongly orthogonal geminals (APSG) approximation is used to check the necessary conditions for the validity of the APSG approximation.
Abstract: The Watson-wave function for the Be ground stats is used to check the necessary conditions — derived previously — for the validity of the antisymmetrized product of strongly orthogonal geminal (APSG) approximation. The agreement between the actual properties of the numerical 1st and 2nd order density matrices and those predicted from the APSG scheme is satisfactory, whereas the predictions made in the framework of the antisymmetrized product of identical geminals (APIG) scheme are not at all realized. “Correlation adapted” orbitals and “generating geminals” are “extracted” from the given numerical wave function. The former are compared with the Edmiston-Ruedenberg localized orbitals, the latter with the Be++ wave functions.
44 citations
TL;DR: In this paper, the Jahn-Teller Theorem wird, im Gegensatz zur Beweisfuhrung von Jahn and Teller, ohne die Notwendigkeit einer detaillierten Diskussion einzelner Symmetrien and ihrer Realisierungsmoglichkeiten durch Atomanordnungen nach dem Muster einer fruher gegebenen Argumentation [4] nochmals bewiesen.
Abstract: Das Jahn-Teller-Theorem wird, im Gegensatz zur Beweisfuhrung von Jahn und Teller, ohne die Notwendigkeit einer detaillierten Diskussion einzelner Symmetrien und ihrer Realisierungsmoglichkeiten durch Atomanordnungen nach dem Muster einer fruher gegebenen Argumentation [4] nochmals bewiesen. Dabei tritt der allen Einzelfallen gemeinsame physikalische Grund fur die Gultigkeit des Theorems in den Vordergrund. Spin-Bahn- und Spin-Spin-Wechselwirkung der Elektronen werden von Anfang an mit berucksichtigt. Der Beweis ohne Zuhilfenahme von Tabellen uber Darstellungen von Normalkoordinaten usw. wird moglich unter Verwendung eines im Anhang abgeleiteten Satzes uber die Induktion von Darstellungen endlicher Gruppen.
TL;DR: In this paper, the static and dynamic Jahn-Teller vibronic couplings in square planar molecules were investigated and it was shown that without spin-orbit coupling and considering only one distorting vibration, the problem can be solved exactly within the Born-Oppenheimer approximation.
Abstract: The static and the dynamic Jahn-Teller vibronic couplings found in square planar molecules are investigated. Without spin-orbit coupling and considering only one distorting vibration, the problem can be solved exactly within the adiabatic Born-Oppenheimer approximation. In this case the vibrational pattern is that expected for a harmonic oscillator. If on the other hand spin-orbit coupling is included the vibrational pattern becomes highly irregular. Finally, in the limit of large spin-orbit coupling the Jahn-Teller coupling is completely quenched and the potential surfaces are again harmonic.
TL;DR: The Selfconsistent Group Orbital and Bond Electronegativity (SGOBE) method for calculating the orbital charge distributions in polyatomic molecules is reviewed and a simplification described in this paper.
Abstract: The Self-consistent Group Orbital and Bond Electronegativity (SGOBE) method [4] for calculating the orbital charge distributions in polyatomic molecules is reviewed, and a simplification described. The charge distributions for several polyatomic molecules are calculated. The chemical significance of the results is discussed.
TL;DR: In this article, the splitting of the two 2.676F states of Yb3+:YAlG and Yb 3+: YGaG, have been determined from fluorescence and absorption spectra at low temperatures.
Abstract: The splitting of the two 2
F states of Yb3+:YAlG and Yb3+:YGaG, have been determined from fluorescence and absorption spectra at low temperatures. The levels of the ground states of Yb3+: YAlG are at: 0, 388, 613, 778 cm−1, those of Yb3+: YGaG at 0, 308, 567, and 672 cm−1. Crystal field calculations yield the following values for Yb3+:YAlG; A
2
0
=270 cm−1, A
4
0
=−165 cm−1, A
4
4
=−1155 cm−1, A
0
6
=21 cm−1, A
4
6
=−304 cm−1 and for Yb3+:YGaG: A
0
2
=110 cm−1, A
0
4
=−125 cm−1, A
4
4
=−1250 cm−1, A
0
6
=10 cm−1 and A
4
6
=−142 −1 A satisfactory agreement has been found for calculated and observed splitting patterns.
TL;DR: The simplified version given by Heilbronner and others of the P-treatment was used to calculate transition energies and intensities of the π − π* bands in the electronic spectra of 31 azines (aza-benzenes and aza-naphthalenes).
Abstract: The simplified version given by Heilbronner and others of the P-treatment was used to calculate transition energies and intensities of the π — π* bands in the electronic spectra of 31 azines (aza-benzenes and aza-naphthalenes). A comparison with experimental data results in a better agreement than for the complete treatment.
TL;DR: In this article, the electronic spectrum of a solution of the copper complex of acetylacetone as well as the spectra observed with polarized light of single crystals of the complex were investigated.
Abstract: The electronic spectrum of a solution of the copper complex of acetylacetone as well as the spectra observed with polarized light of single crystals of the complex are reinvestigated. The observed bands are interpreted by the crystal-field theory.
TL;DR: In this paper, the Franck-Condon factors are calculated on the assumption that the frequencies and normal modes in the ground and excited states are identical and show that the assumption (by McCoy and Ross) that the C-C stretching frequencies are degenerate is satisfactory as far as the calculation of the overall vibrational envelope is concerned.
Abstract: Progressional intensities have been calculated for the 1
L
a band of the polyacenes which give good agreement with experiment The Franck-Condon factors are calculated on the assumption that the frequencies and normal modes in the ground and excited states are identical Our results, based on a simple force field, also show that the assumption (by McCoy and Ross) that the C-C stretching frequencies are degenerate is satisfactory as far as the calculation of the shape of the overall vibrational envelope is concerned
TL;DR: In this paper, die Energie des Grundzustandes unter Einschlus der Elektronenwechselwirkung wurde bezuglich des Index l der Legendrefunktionen und des Parameters q der Hillfunktions minimisiert.
Abstract: Funferheterozyklen mit einem Heteroatom wurden mit einer Einzentrenmethode behandelt. Als Einteilchenfunktionen wurde eine Basis von orthogonalen Funktionen in Kugelkoordinaten gewahlt, die sich uber das ganze Molekul erstrecken und am Mittelpunkt des Funfrings zentriert sind. Als Radialfunktionen wurden Slaterfunktionen, als ϑ-Winkelfunktionen geeignete Legendrefunktionen und als ϕ - Winkelfunktionen zur Berucksichtigung des Heteroatoms Hillfunktionen gewahlt. Die Energie des Grundzustandes unter Einschlus der Elektronenwechselwirkung wurde bezuglich des Index l der Legendrefunktionen und des Parameters q der Hillfunktionen minimisiert. Elektronendichte, Dipolmoment, Ubergangsmomente, Anregungsenergien und Diamagnetismus liesen sich quantitativ erfassen, die Ionisationsenergie nicht.
TL;DR: In this paper, a 3-dimensional FEM wird zur Berechnung von Bindungseigenschaften zwei-and mehratomiger Molekule vorgeschlagen, das lediglich die Kenntnis der Atomradien voraussetzt.
Abstract: Ein 3-dimensionales FEM wird zur Berechnung von Bindungseigenschaften zwei- und mehratomiger Molekule vorgeschlagen, das lediglich die Kenntnis der Atomradien voraussetzt. Die Reihenfolge und Entartung analoger Terme beim FE-Modell einerseits und einfachen MO-Modell andererseits sind gleich. Die Einfachheit des Modells beruht auf der Existenz einer geschlossenen Eigenwertformel und auf der leicht uberschaubaren Gestalt der FE-MOs, die eine ausfuhrliche Diskussion der jeweiligen Elektronenverteilung (Elektronenpopulationsanalyse) gestatten. Das Modell liefert auch Anregungsenergien (Elektronenspektren) und magnetische Eigenschaften. Die Berechnungen wurden fur 120 zweiatomige homonukleare Molekule A2 bzw. Molekulionen A
2
±
sowie fur eine Reihe linearer mehratomiger Molekule durchgefuhrt. Schlieslich findet eine kritische Gegenuberstellung des dreidimensionalen Modells mit dem zwei- bzw. eindimensionalen Modell statt.
TL;DR: In this article, it was shown that the alternant molecular orbital method can be entirely fitted into the separated-pair theory and the total wave function can be taken as a linear combination of antisymmetrized product functions constructed of strongly orthogonal geminals.
Abstract: It is shown that the alternant molecular orbital method can be entirely fitted into the separated-pair theory The total wave function can be taken as a linear combination of antisymmetrized product functions constructed of strongly orthogonal geminals In the single parameter case, however, these strongly orthogonal geminals cannot be uniquely defined by the criterion of minimum energy alone The separated-pair formalism may prove more favorable when the one-electron basis is to be extended in order to include, e g, “vertical” correlation effects
TL;DR: It is shown that the group-theoretic vibronic selection rules given by DIJKGaAA~ are equivalent to those used by PIrER and BEL~O~D and discussed some features of the energy level scheme and spectra.
Abstract: In a recent publication, DIJKORAAF [1] proposed an exciton interpretation of the crystal spectra of copper acetylaeetone. Although it is possible that the bands observed in molecular crystals of some metal chelates do show Davydov splitting, as DI5KG~AAF believes, several considerations make it unlikely that copper aeetylaeetone is such a ease. FEiGn;SON [6] discusses some of these considerations ; in this paper we point out another. Furthermore, there are some other features of DIJKGRAAF'S treatment which require clarification. In this paper, we begin by showing that the group-theoretic vibronic selection rules given by DIJKGaAA~ [1] are equivalent to those used by PIrER and BEL~O~D [6]. We then discuss some features of the energy level scheme and spectra.
TL;DR: In this article, a Verfahren beschrieben, das die Tensoren der Kernquadrupolkopplung und der paramagnetischen Hyperfeinstruktur in Einkristallen beliebiger Symmetrie aus Kernresonanz-messungen in mittleren Magnetfeldern zu bestimmen gestattet.
Abstract: Es wird ein Verfahren beschrieben, das die Tensoren der Kernquadrupolkopplung und der paramagnetischen Hyperfeinstruktur in Einkristallen beliebiger Symmetrie aus Kernresonanz-messungen in mittleren Magnetfeldern zu bestimmen gestattet. Mogliche Anwendungen des Verfahrens in der paramagnetischen Elektronenresonanz werden diskutiert.
TL;DR: In this paper, the electronic absorption spectra of the n-heptane and ethanol solutions and the polarized absorption spectrum of the single crystal were measured with 1,5-dinitronaphthalene.
Abstract: The electronic absorption spectra of the n-heptane and ethanol solutions and the polarized absorption spectrum of the single crystal were measured with 1,5-dinitronaphthalene. 1,5-Dinitronaphthalene shows three absorption bands at 198.7, 230 and 323 mμ. The 230 mμ and 323 mμ. bands are polarized almost parallel with the long and short axes of the naphthalene ring respectively. The assignment of the bands has been made by combining the observed results with the theoretical consideration.
TL;DR: In this article, a zweiparametrige Eigenwert-Differentialgleichung fur die von der ersten elliptischen Koordinate μ abhangige Funktion U(μ) auf is discussed.
Abstract: Bei der Separation der Schrodinger-Gleichung fur ein Elektron im Feld zweier festgehaltener Punktladungen tritt eine zweiparametrige Eigenwert-Differentialgleichung fur die von der ersten elliptischen Koordinate μ abhangige Funktion U(μ) auf. Fur U(μ) wurden von Hylleraas (1931) und von Jaffe (1933) Reihenentwicklungen angesetzt, deren Koeffizienten jeweils als Eigenvektoren einer von der benutzten Basis abhangigen Jacobischen Matrix zu bestimmen sind. In dieser Arbeit wird bewiesen, das die aus den beiden Ansatzen resultierenden Matrizen dieselben Eigenwertkurven besitzen. Unter der Annahme, das das Verhaltnis RZ/p ungleich einer naturlichen Zahl ist, wird eine nur von diesem Verhaltnis abhangige regulare Diagonalmatrix konstruiert, welche die zwei Matrizen ineinander transformiert sowie deren geeignet normierte Eigenvektoren, also die Koeffizientensatze der zwei Entwicklungen, ineinander uberfuhrt.
TL;DR: Using molecular orbital theory and experimental bond orders, valency structures for C2O2−4 S2O 2−4 and cis (CH3NO)2 were deduced in this article.
Abstract: Using molecular orbital theory and experimental bond orders, valency structures for C2O2−4 S2O2−4 and cis (CH3NO)2 are deduced. For the latter system, the wave function for a structure that violates the octet rule for the first row elements is contrasted with that pertaining to the double quartet hypothesis [14].
TL;DR: Using Brion, Moser and Yamazaki's SCF LCAO MO the spin orbit splitting of the X2Π state of NO has been calculated using various potentials as discussed by the authors.
Abstract: Using Brion, Moser and Yamazaki's SCF LCAO MO the spin orbit splitting of the X2Π state of NO has been calculated using various potentials. Experimentally W (2Π3/2) −W (2Π1/2) is known to be 122 cm−1. Using an “unscreened” nuclear field we find a value of 328 cm−1. Inclusion of screening due to electronic repulsions reduces this value to 283 cm−1. Agreement with the experimental value may be obtained by reducing the orbital exponents in the 2π molecular orbital by 30% over the value given by Slater's rules.
TL;DR: In this paper, a simple expression, differing from the one currently used, must be adopted when calculating π electron spin densities from unrestricted H.F. wave functions in connection with the prediction of proton hyperfine couplings in aromatic free radicals.
Abstract: It is shown that a simple expression, differing from the one currently used, must be adopted when calculating π electron spin densities from unrestricted H.F. wave functions in connection with the prediction of proton hyperfine couplings in aromatic free radicals. The proposed formula gives results which are almost identical to those one obtains after complete projection of the unwanted parts of the unrestricted function.