Energy levels and crystal-field calculations of trivalent ytterbium in yttrium aluminum garnet and yttrium gallium garnet

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.

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Zusammenfassung Die Aufspaltung der ² F-Zustände von Yb³⁺:YAlG(I) und Yb³⁺:YGaG (II) wurde bei tiefen Temperaturen aus Fluoreszenz- und Absorptionsspektren bestimmt. Die Niveaus des Grundzustandes von (I) liegen bei 0, 388, 613, 778 ^–1, die von (II) bei 0, 308, 567 und 672 ^–1. Die Ligandenfeldtheorie ergibt folgende Werte für die Kristallfeldparameter: für (I) 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 unf für (II) A ₀ ² =110 cm^–1, A ₀ ⁴ =–125 cm^–1, A ₄ ⁴ =–1250 cm^–1, A=10 cm^–1 and A ₄ ⁶ =–142 ^–1. Die Übereinstimmung zwischen berechneter und beobachteter Aufspaltung war befriedigend.

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Résumé La division, par le champ de ligandes, des états ² F _7/2 et ² F _5/2 dans Yb³⁺:YAlG et Yb³⁺:YGaG a été déterminée des spectres de fluorescence et d'absorption. Les sous-niveaux de l'état fordamental se situent à 0, 388, 613, 778 cm^–1 dans Yb³⁺:YAlG, à 0, 308, 567, 672 cm^–1 Yb³⁺: YGaG. Le calcul fournit les valeurs suivantes pour les paramètres: 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 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 et A ₄ ⁶ =–142 ^–1. L'accord entre les spectres calculé et observé est satisfaisant.

     

On the reliability of equilibrium data of the charge-transfer complex between 2,3-dichloro-1,4-naphthoquinone and hexamethylbenzene

In view ofHammond's warning⁶ about the Conspiracy of errors, found in the case of low values of equilibrium constants of charge-transfer complexes a case is made out for redetermining the values for the system hexamethylbenzene—2,3-dichloro-1,4-naphthoquinone. Uncertainties in the parameters were estimated using theLiptay ⁸ matrix procedure. The solvent used was dichloromethane. The following data were obtained at 25°C: vC T = 22,220 cm^–1;E _A=0.99 eV;K =2599±57 l²·cm^–1·mol^–2. _max= 1020 ± 148 cm^–1··1;K=2.55±0.37 l·mol^–1; –H=2.7±0.3 kcal·mol^–1.With 1 Figure     

Low temperature absorption spectra of KMnO4 in KClo4

The permanganate spectrum has been remeasured at liquid hydrogen and helium temperatures using spectrographs with reasonably high dispersion. Evidence is found for four absorption band systems. The first one is assigned as ¹ A ₁ ¹ T ₂ and displays a great deal of vibrational structure starting with the 0–0 line located at 18,072 cm^–1. The second transition found at 25,000 to 30,000 cm^–1 is rather featureless. The third transition with maximum at 33,000 cm^–1 shows a simple progression in quanta of 750 cm^–1. The fourth band is completely featureless with maximum intensity at 43,500 cm^–1. These findings are compared with a simplified SCF LCAO MO calculation.

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Zusammenfassung Das Permanganat-Spektrum wurde bei Temperaturen von flüssigem Wasserstoff und Helium unter Verwendung eines ausreichend auflösenden Spektrographen neu vermessen, wobei vier Absorptionssysteme gefunden wurden. Dem ersten von ihnen wurde ein ¹ A ₁ ¹ T ₂-Übergang zugeordnet; es besitzt eine ausgeprägte Vibrationsstruktur (0–0-Bande bei 18,072 cm^–1, während das folgende zwischen 25,000 und 30,000 cm^–1 kaum eine Struktur zeigt. Der dritte Übergang mit Maximum bei 33,000 cm^–1 zeigt einfache Progressionen entsprechend Quanten von 750 cm^–1. Die vierte Bande schließlich ist vollkommen strukturlos und hat ihr Maximum bei 43,500 cm^–1. Diesen Daten wurden die Ergebnisse einer einfachen SCF-LCAO-MO-Rechnung gegenübergestellt.

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Résumé Le spectre du permanganate de potassium a été réétudié aux températures de l'hydrogène et de l'hélium liquide en utilisant des spectrographes à dispersion raissonnablement élevée. On trouve la preuve de la présence de quatre systèmes de bandes d'absorption. Le premier, attribué à ¹ A ₁ ¹ T ₂, possède une forte structure vibrationnelle commencant à la bande 0–0 située à 18.072 cm^–1. La seconde transition située entre 25.000 et 30.000 cm^–1 est plutot sans structure. La troisième transition avec un maximum à 33.000 cm^–1 présente une progression simple de 750 cm^–1. La quatrième bande est complètement sans structure et a son maximum vers 43.500 cm^–1. Ces observations sont comparées avec un calcul simplifié SCF LCAO MO.

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NATO Postdoctoral Fellow 1965–66.     

Low temperature absorption spectra of CrO 4 = in K2SO4 and VO 4 ≡ in Na3PO4 · 12H2O

The polarized absorption spectrum of the chromate ion has been measured at liquid hydrogen and helium temperatures. With chromate dissolved in K₂SO₄ evidence is found for two orbitally allowed ¹ A ₁¹ T ₂ electronic absorption bands. The first band is split into three sublevels with the 0-0 lines located at 26,316 cm^–1, 26,441 cm^–1 and 26,610 cm^–1. Built upon the 0-0 lines is seen a simple progression in quanta of 783 cm^–1. The second transition is nearly featureless, and is found at 34,000 cm^–1 to 44,000 cm^–1. The two bands are assigned as primarily t ₁2e and as 3t ₂2e respectively.VO ₄ dissolved in Na₃PO₄ · 12H₂O showed at liquid nitrogen temperature a broad featureless band found between 30,000 and 40,000 cm^–1.

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Zusammenfassung Das polarisierte Absorptionsspektrum des Chromations wurde bei den Temperaturen des flüssigen Wasserstoffs und Heliums gemessen. Für Chromat in K₂SO₄ werden zwei erlaubte Absorptionsbanden ¹ A ¹¹ T ₂ gefunden. Die erste Bande ist dreifach aufgespalten, ihre 0-0 Linien liegen bei 26316 cm^–1, 26441 cm^–1 und 26610 cm^–1. Von den 0-0 Linien ausgehend zeigt sich eine einfache Zunahme der Werte um 783 cm^–1. Der zweite Übergang ist nahezu strukturlos, er liegt zwischen 34000 cm^–1 und 44000 cm^–1. Die beiden Banden werden überwiegend t ₁2e bzw. 3t ₂2e zugeordnet. VO ₄ in Na₃PO₄ · 12H₂O zeigt bei der Temperatur des flüssigen Stickstoffs eine breite strukturlose Bande zwischen 30 000 und 40 000 cm^–1.

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Résumé Le spectre d'absorption en lumière polarisée de l'ion chromate a été mesuré aux températures de l'hydrogène et de l'hélium liquide. Pour le chromate dissous dans K₂SO₄ on met en évidence deux bandes d'absorption électronique de transition orbitale permise ¹ A ₁¹ T ₂. La première bande est séparée en trois sous niveaux dont les raies 0-0 se trouvent à 26,316 cm^–1, 26,441 cm^–1 et 26,610 cm^–1. A partir des raies 0-0 on distingue une période de 783 cm^–1. La seconde bande est presque non structurée et s'étend de 34,000 cm^–1 à 44,000 cm^–1. Les deux bandes sont décrites comme t ₁2e et 3t ₂2e respectivement.VO ₄ dissous dans Na₃PO₄ · 12H₂O révèle à la température de l'azote liquide une large bande sans structure entre 30,000 et 40,000 cm^–1.

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On leave of absence from Anorganisch Chemisch Laboratorium der Universiteit, Amsterdam.     

IR study of cation effects on the O-D stretching frequencies of isotopically dilute HDO in aqueous salt solutions

IR spectra of 3 normal solutions of 14 different salts [chlorides of Al⁺⁺⁺, Be⁺⁺, Mg⁺⁺, Ca⁺⁺, Sr⁺⁺, Ba⁺⁺, Zn⁺⁺, Cd⁺⁺, Li⁺, Na⁺, K⁺, Rb⁺, Cs⁺, N(CH₃) ₄ ⁺ ] in both, 96% H₂O+4% D₂O and 100% H₂O, were measured in the frequency range =2 800–2 100 cm^–1. From up to 18 single measurements for each solution the frequencies and halfwidths of the O-D stretching bands of isotopically dilute HDO were determined with high accuracy. Frequencies in the range =2 510–2 529 cm^–1 and halfwidths in the range =155–205 cm^–1 resulted atT=30°C with standard deviations typical less than ±1 cm^–1 and ±4 cm^–1, respectively. An almost perfect correlation between the O-D stretching band parameters and the polarizing power of the cations was obtained.Herrn Prof. Dr.A. Neckel, Wien, zum 60. Geburtstag gewidmet.     

Calcul par double perturbation de l'interaction dipolaire spin-spin dans les molécules

Résumé Les paramètres D et E de molécules dans l'état triplet sont calculés par double perturbation au premier ordre par rapport à l'hamiltonien de corrélation de P. S. Epstein, et à l'hamiltonien d'interaction dipolaire spin-spin. On montre que les seules configurations diexcitées triplets fournissant une contribution non nulle sont celles où les orbitales occupées par un seul électron dans le plus bas triplet deviennent vides ou doublement occupées. On trouve ainsi pour le naphtalène D= 0,090 cm^–1, E=–0,014 cm^–1 (exp = D=0,100 cm^–1, E=–0,014 cm^–1). La polarisation de spin seule donne D=0,113 cm^–1, E= –0,027 cm^–1. La contribution du 2ème ordre par rapport à la perturbation due à la corrélation est évaluée à 10% de D total.

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Calculation of the dipolar spin-spin interaction by double perturbation theory in moleculesApplication to the triplet states of hydrocarbons

A double perturbation calculation of D and E parameters of molecular triplet states is performed in first order with respect both to correlation (as defined by P. S. Epstein) and dipolar spin-spin interaction. A non zero contribution is obtained from diexcited triplet configurations only if the singly occupied orbitals of the lowest triplet configuration become either empty or doubly occupied. Results are for Naphtalene: D=0.090 cm^–1, E=–0.014 cm^–1 (exp: D=0.100 cm^–1, E=–0.014 cm^–1). Spin polarization alone yields D=0.113 cm^–1, E=–0.027 cm^–1. The correlation second order contribution for D is estimated to 10% of the over-all value.

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Zusammenfassung Es wird eine Berechnung des D- und E-Parameters molekularer Triplettzustände im Rahmen einer zweifachen Störungsrechnung bis zur ersten Ordnung durchgeführt, und zwar sowohl in bezug auf die Korrelation (wie definiert von P. S. Epstein) als auch die dipolare Spin-Spin-Wechselwirkung. Der Beitrag zweifach angeregter Triplettkonfigurationen ist nur dann von Null verschieden, wenn die beiden in der Grundkonfiguration einfach besetzten Orbitale entweder gar nicht oder doppelt besetzt sind. Die Ergebnisse für Naphthalin sind: D=0,090 cm^–1, E=–0,014 cm^–1 (exp.: D=0,100 cm^–1, E=–0,014 cm^–1), während die Spinpolarisation allein D=0,113 cm^–1, E=–0,027 cm^–1 liefert. Der Beitrag der Korrelation zu D in zweiter Ordnung wird auf 10% des Gesamtwertes geschätzt.

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Travail effectué dans les cadres de la Convention N-67-34217-00-480-75-01 de la Direction des Recherches et Moyens d'Essais (Responsable: Prof. B. Pullman).     

Vibrational spectra,conformational stability,barriers to internal rotation,r0 structural parameters and ab initio calculations of fluoromethyl methyl ether

The far-infrared spectrum of gaseous fluoromethyl methyl ether, FCH₂OCH₃, along with three of the deuterium isotopes, has been recorded at a resolution of 0.10 cm^–1 in the 350 to 50 cm^–1 region. The fundamental asymmetric torsional and methyl torsional modes are extensively mixed and have been observed at 182 and 132 cm^–1, respectively, for the stablegauche conformer with the lower frequency band having several excited states falling to lower frequency. An estimate is given for the potential function governing the asymmetric rotation. On the basis of a one-dimensional model the barrier to internal rotation of the methyl moiety is determined to be 527±9 cm^–1 (1.51±0.03 kcal/mol). A complete assignment of the vibrational fundamentals for all four isotopic species observed from the infrared (3500 to 50 cm^–1) spectra of the gas and solid and from the Raman (3200 to 10 cm^–1) spectra of the gas, liquid, and solid is proposed. No evidence could be found in any of the spectra for the high-energytrans conformer. All of these data are compared to the corresponding quantities obtained from ab initio Hartree-Fock gradient calculations employing the 3-21G and 6-31G* basis sets along with the 6-31G* basis set with electron correlation at the MP2 level. Additionally, completer ₀ geometries have been determined from the previously reported microwave data and carbon-hydrogen distances determined from infrared studies. The heavy-atom structural parameters (distances in Å, angles in degrees) arer(C₁-F) = 1.395 ± 0.005;r(C₁-O) = 1.368 ± 0.007;r(C₂-O) = 1.426 ±0.003; FC₁O = 111.33 ± 0.25; C₁OC₂ = 113.50 ± 0.18 and dih FC₁OC₂ = 69.12 ± 0.26. All of these results are discussed and compared with the corresponding quantities obtained for some similar molecules.     

Far-Infrared Spectra, Conformational Stability, Barriers to Internal Rotation, Ab Initio Calculations, r0 Structural Parameters, and Vibrational Assignment of Ethyl Methyl Ether

The far-infrared spectra (350–35 cm^–1) of gaseous ethyl methyl ether-d ₀ and ethyl methyl-d ₃-ether have been recorded at a resolution of 0.10 cm^–1. For the d ₀ species, the fundamental asymmetric torsion of the more stable trans conformer (two methyl moieties are trans to one another) has been observed at 115.40 cm^–1 with four upper state transitions falling to lower frequency, whereas, for the gauche form, it has been observed at 93.56 cm^–1 with two excited states falling to lower frequency. the corresponding series for the d ₃ species start from 106.00 and 87.10 cm^–1, respectively. From these data, the asymmetric torsional potential coefficients for the d ₀ species have been determined to be: V ₁ = 572 ± 30; V ₂ = 85 ± 8; V ₃ = 619 ± 30; V ₄ = 175 ± 18, and V ₆ = –28 ± 3 cm^–1. The trans to gauche and gauche to gauche barriers were calculated to be 958 cm^–1 (11.5 kJ/mol) and 631 cm^–1 (7.55 kJ/mol), respectively, with an energy difference of 550 ± 6 cm^–1 (6.58 ± 0.07 kJ/mol). Utilizing three conformer pairs, variable temperature studies (–105 to –150°C) of the infrared spectra of the d ₀ sample dissolved in liquid krypton gave an enthalpy difference of 547 ± 28 cm^–1 (6.54 ± 0.33 kJ/mol) with the trans conformer the more stable rotamer. It is estimated that there is only 4% of the gauche conformer present at ambient temperatures. The structural parameters, conformational stabilities, barriers to internal rotation, and fundamental vibrational frequencies, which have been determined experimentally, are compared to those obtained from ab initio gradient predictions from RHF/6-31G* and with full electron correlation at the MP2 level with three different basis sets. The adjusted r ₀ structural parameters have been obtained for the trans conformer from combined ab initio MP2/6-311+G** predictions and previously reported microwave rotational constants. The reported distances should be accurate to 0.003 Å and the angles to 0.5°. These results are compared to the corresponding quantities obtained for some similar molecules.     

Magnetic properties of transition metal ion cubic 5T2 terms in axial ligand fields

The theory of magnetic anisotropy and susceptibility is worked out for cubic ⁵T₂ terms, the degeneracy of which is partially lifted by a ligand field component of axial symmetry as well as by spin-orbit coupling. Matrix elements are calculated by application of the method of Abragam and Pryce to a set of M.O. based wave-functions. The anisotropy in covalency of the metal-ligand bond and in spin-orbit coupling is taken into account. Numerical values of principal magnetic moments, P and P , are calculated as function of kT/, /, and .The theoretical results are employed in a rigorius analysis of existing single crystal magnetic data on high-spin iron(II) compounds. For (NH₄)₂Fe(SO₄)₂·6 H₂O, =–100 cm^–1, =1070 cm^–1 and =0.8 to 0.6 is obtained. For FeSiF₆·6 H₂O, =–80 cm^–1, =–760cm^–1 at 77.3K and –580 cm^–1 between 20.4 and 1.57K, and 0.7 is derived. No unique fit is possible for K₂Fe(SO₄)₂·6 H₂O. The data are reproduced to better than ±1% in most cases. The limitations of the approach are stressed.

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Zusammenfassung Die Theorie der magnetischen Anisotropie und der magnetischen SuszeptibilitÄt eines ⁵ T ₂ Grundterms im oktaedrischen Ligandenfeld wird für den Fall entwickelt, da\ die Entartung unter dem Einflu\ einer axial-symmetrischen Feldkomponente sowie der Spin-Bahn-Wechselwirkung teilweise aufgehoben ist. Eigenfunktionen werden auf der Grundlage der M.O.-Theorie aufgestellt, Matrixelemente mittels der Theorie von Abragam und Pryce ermittelt. Der Anisotropie der Metall-Ligand-Bindung sowie der Spin-Bahn-Kopplung wird Rechnung getragen. Numerische Werte für die magnetischen Hauptmomente P und P werden in AbhÄngigkeit von kT/, / und berechnet.Die Ergebnisse der Theorie werden für eine genaue Analyse der verfügbaren magnetischen Daten aus Messungen an Einkristallen magnetisch normaler Eisen(II)-Verbindungen verwendet. Für (NH₄)₂Fe(SO₄)₂·6 H₂O werden =–100 cm^–1, = 1070 cm^–1 und = 0,8 bis 0,6 erhalten. Für FeSiF₆·6 H₂O ergeben sich =–80 cm^–1, =–760 cm^–1 bei 77,3K und =–580 cm^–1 zwischen 20,4 und 1,57K sowie 0,7. Die experimentellen Daten können in den meisten FÄllen auf ±1% genau oder besser wiedergegeben werden. Bei K₂Fe(SO₄)₂·6 H₂O gelang keine eindeutige Bestimmung der theoretischen Parameter. Die Grenzen der vorliegenden Behandlung werden kritisch diskutiert.

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Résumé La théorie de l'anisotropie magnétique et de la susceptibilité magnétique est développée pour les termes cubiques ⁵ T ₂, dont la dégénérescence est partiellement levée par une composante à symétrie axiale du champ de ligandes ainsi que par le couplage spin-orbite. Les éléments de matrice sont calculés à l'aide de la méthode d'Abragam et Pryce employée sur un système M.O. des fonctions d'onde de base. On a pris en consideration l'anisotropie de la liaison entre le metal et le ligand et aussi du couplage spin-orbite. Les valeurs numériques des moments magnétiques principaux P et P sont calculées en fonction de kT/, /, et .Les résultats théoriques sont employés dans une analyse détaillée des données magnétiques disponibles sur monocristaux des composés ferreux spin-élevés. Pour (NH₄)₂Fe(SO₄)₂·6 H₂O on a obtenu =–100 cm^–1, =1070 cm^–1 et =0.8 à 0,6. Pour FeSiF₆·6 H₂O on a eu comme résultat =–80 cm^–1, =–760 cm^–1 à 77,3 K et =–580 cm^–1 entre 20,4 et 1,57K avec 0,7. Les valeurs expérimentales sont réprésentées dans la plupart de cas plus précises que ±1%. Au cas de K₂Fe(SO₄)₂·6 H₂O une détermination unique était impossible. Les limites de cette approximation sont discutées.

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Postdoctoral Fellow, Theoretical Chemistry, 1963–1964.     

A vibrational analysis of the MnO 4 − bands

Teltow'S [14,15] measurements of the permanganate bands are reanalyzed using the level scheme of Ballhausen and Liehr [2]. For KMnO ₄ dissolved in KClO ₄ the components of the first ¹ T ₂ state are found at 18050 cm^–1 18078 cm^–1 and 18043 cm^–1. The breathing frequency of the MnO _– ⁴ unit is in this state 768 ^–1. The electronic origin of the second ¹ T ₂ state is found at 30723 cm^–1 with a breathing frequency of 760 cm^–1.Evidence is further found for a ¹ T ₁ state with its split components located at 14446 cm^–1, 14526 cm^–1 and 14600 cm^–1. The breathing frequency is here found to be 800 cm^–1.Finally for KMnO ₄ dissolved in NaClO ₄ there are indications that one or two spin-triplets are located near 13200 cm^–1.

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Zusammenfassung TeltowS Messungen des Permanganatspektrums [14, 15] werden mit Hilfe des Termschemas von Ballhausen und Liehr [2] von neuem analysiert. Für KMn ₄ in KClO ₄ findet man die zum ersten ¹ T ₂-Zustand gehörenden Komponenten bei 18050, 18078 und 18043 cm^–1. Die Valenzschwingung des MnO _– ⁴ liegt hier bei 768 cm^–1. Der Ursprung des zweiten ¹ T ₂-Systems wird bei 30723 cm^–1 gefunden, die dazugehörige Valenzfrequenz ist 760 cm^–1.Bei 14446, 14526 und 14600 cm^–1 liegen offenbar die Komponenten eines ¹ T ₁-Terms, wozu eine Valenzfrequenz von 800 cm^–1 gehört.Schließlich findet man für KMnO ₄ in NaClO ₄ Anzeichen für ein oder zwei Spin-Tripletts um 13200 cm^–1.

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Résumé Les bandes d'absorption du permanganate, mesurées par Teltow [14,15], sont réanalysées à l'aide d'un système de termes proposé par Ballhausen et Liehr [2]. Pour KMnO ₄ dans KClO ₄, on trouve les composants du premier état ¹ T ₁ à 18050, 18078 et 18043 cm^–1. La vibration symétrique du MnO _– ⁴ dans cet état se situe à 768 cm^–1. L'origine électronique du second état ¹ T ₂ est trouvé à 30723 cm^–1, la fréquence oscillatrice correspondante est de 760 cm^–1.Un état ¹ T ₁ avec ses composants à 14446, 14526 et 14600 cm^–1 est mis en évidence, avec une vibration symétrique de 800 cm^–1.Finalement, au cas du KMnO ₄ dissous dans le NaClO ₄, il y a des indications pour un ou deux triplets de spin vers 13200 cm^–1.

     

FT-Raman Study of Ionic Interactions in Lithium and Silver Tetrafluoroborate Solutions in Acrylonitrile

Solutions of silver and lithium tetrafluoroborate in acrylonitrile, over a range ofconcentrations between 0.5 and 4 mol-kg^–1, have been studied byFourier-transform Raman spectroscopy. The spectral regions studied include the solvent(C=dN) fundamental and the anion B-F symmetric stretching band. In AgBF₄solutions the absence of ionic pairing was demonstrated and the anion ₁(A ₁)remains as a single narrow band located at 764.7±0.1 cm^–1. Consequently, thesilver ion solvation number does not change in the range of concentrations studied,having a constant value of 3.54±0.10. However, a high level of ionic pairingwas observed in the corresponding solutions of LiBF₄. Three components weredetected in the tetrafluoroborate ₁(A ₁) band located at 766.0±0.4, 773.4±1.1,and 782.7±0.9 cm^–1, and assigned to spectroscopically free anions, ion pairs,and dimers, respectively. The solvation number of the lithium ion, which shouldbe three in the limit of infinite dilution, decreases as the salt concentrationincreases as a result of the ionic pairing. However, the ionic pairing of LiBF₄ inacrylonitrile is less than that previously observed in lithiumtrifluoromethanesulfonate (triflate) or lithium perchlorate.     

Ein 3-dimensionales FE-Modell der chemischen Bindung

Zusammenfassung Ein 3-dimensionales FEM wird zur Berechnung von Bindungseigenschaften zwei- und mehratomiger Moleküle 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 überschaubaren Gestalt der FE-MOs, die eine ausführliche Diskussion der jeweiligen Elektronenverteilung (Elektronenpopulationsanalyse) gestatten. Das Modell liefert auch Anregungsenergien (Elektronenspektren) und magnetische Eigenschaften. Die Berechnungen wurden für 120 zweiatomige homonukleare Moleküle A₂ bzw. Molekülionen A ₂ ^± sowie für eine Reihe linearer mehratomiger Moleküle durchgeführt. Schließlich findet eine kritische Gegenüberstellung des dreidimensionalen Modells mit dem zwei- bzw. eindimensionalen Modell statt.

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A free electron model for diatomic molecules for which only the atomic radius has to be known is proposed. Corresponding terms of the FE- and the simple MO model occur in the same order and with the same degeneration. The model is very simple because it implies a formula for eigen values and state functions which can be easily handled (population analysis). Electronic spectra and magnetic properties can be calculated. 120 molecules of Type A₂, A ₂ ⁺ , A ₂ ^– , and A _n (linear) were treated in this way. Finally models with one, two, and three dimensions are compared.

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Résumé Nous proposons un modèle spatial des électrons libres pour le calcul de atomiques molécules di- et polyatomiques où les rayons sont les seuls paramètres. L'ordre des niveaux est analogue à celui du modèle MO simple. Le modèle est facile à traiter, parce qu'il conduit à une formule close pour les valeurs propres et à des orbitales simples. Ceci facilite la discussion de la distribution d'électrons, des spectres et des propriétés magnétiques. Nous avons calculé 120 molécules et ions des types A₂, A ₂ ⁺ et A ₂ ^– , et d'autres du type A _n , linéaires. Les modèles à une, deux et trois dimensions sont comparés.

     

The kinetics of vapor-phase nitration of cellulose 2. Nitration with nitric acid under static conditions

The regularities of vapor-phase nitration of cellulose with HNO₃ under conditions of natural convection and hindered heat removal in the absence of air were studied using the nonisothermal kinetic method. It was established that the nitration rate at the depth of conversion of 0.08 to 0.7 is described by the kinetic law d/dt =k ₁ p/(1+), wherek ₁ = 10^4.49±0.6 exp(–A/RT) s^–1 atm^–1, = 10^{–35.5±15.7}exp(B/RT),A = 36.6±3.8 kl mol^–1, andB = 203±88 kJ mol^–1. The diffusion mechanism of vapor-phase nitration of cellulose, which explains the high value of activation energies, is discussed. The effective diffusion coefficient of HNO₃ in cellulose at 25 °3.7 · 10^–7 cm² s^–1) and the activation energy of diffusion (38.3±4.2 kJ mol^–1) were estimated.For Part 1, see Ref. l.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1981–1985, August, 1996.     

The2 E↔4 A 2 transition in tetragonal Cr3+ complexes

The² E⁴ A ₂ absorption and emission spectra of [Cr(NH₃)₅(NO₃)](NO₃)₂, [Cr(NH₃)₅(NO₂)] ·(NO₃)₂, and [Cr(NH₃)₅(H₂O)](NO₃)₃ microcrystals have been recorded at 77°K. Tetragonal²E splittings are 209, 188 and 87 cm^–1, respectively. An analysis of the limited vibronic structure has been made and compared to the results for the parent octahedral complex, [Cr(NH₃)₆](NO₃)₃. Vibrations of approximately 270 and 700 cm^–1 are prominent.

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Zusammenfassung Die² E⁴ A ₂ Absorptions- und Emissionsspektren von [Cr(NH₃)₅(NO₃)](NO₃)₂-, [Cr(NH₃)₅ (NO₂)](NO₃)₂- und [Cr(NH₃)₅(H₂O)](NO₃)₃-Mikrokristallen werden für 77° angegeben. Die tetragonalen² E Aufspaltungen sind209, 188 bzw. 87 cm^–1. Eine Analyse der begrenzten vibronischen Struktur wurde vorgenommen und mit den Resultaten für den oktaedrischen Stammkomplex, [Cr(NH₃)₆](NO₃)₃ verglichen. Schwingungen von etwa 270 und 700 cm^–1 treten besonders hervor.

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Résumé Les spectres d'émission et d'absorption² E⁴ A ₂ de microcristaux de [Cr(NH₃)₅(NO₃)](NO₃)₂, [Cr(NH₃)₅(NO₂)](NO₃)₂ et [Cr(NH₃)₅(H₂O)](NO₃)₃ ont été enregistrés à 77° K. Les écartements tétragonaux² E sont respectivement 209, 188 et 87 cm^–1. Une analyse de la structure vibronique limitée a été effectuée et comparée aux résultats pour le complexe octaédral parent [Cr(NH₃)₆](NO₃)₃. Les vibrations au voisinage de 270 et 700 cm^–1 émergent.

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This contribution is dedicated to the memory of Prof. Hans-Ludwig Schläfer, a stimulating colleague and valued friend.     

Spectra and structure of small ring compounds. LIX

The Raman (3200 to 10 cm^–1) and far infrared (380 to 60 cm^–1) spectra of gaseous fluorocyclobutane,c-C₄H₇F, have been recorded. A series of Q-branches observed in both of these spectra beginning at 166 cm^–1 with successive transitions falling to lower frequencies have been assigned to the ring puckering vibrations of both the low energy equatorial and high energy axial conformers. These data have been fit to an asymmetric potential function of the form:V (cm^–1)=(1.76±0.05)10³X+(4.88±0.28)10⁴X²+(2.12 ±0.16)10³ exp(–5.66±0.41)10X² with a reduced mass function ofg ₄₄= 0.00386–0.00295X+0.03485X²+0.1228X³ +0.3459X⁴, whereX is the ring puckering coordinate. Utilizing this potential, the difference between the puckering angles for the two conformers was calculated to be 4° with the equatorial conformer having the larger value of 28°. This potential function is consistent with an energy difference between the equatorial and axial forms of 447 cm^–1 (1.28 kcal/mol) and a barrier to ring inversion from the equatorial to the axial conformation of 713 cm^–1 (2.04 kcal/mol). Experimental values for the enthalpy difference between the two conformers have been determined for both the liquid (400±30 c^–1) and gas (413±43 cm^–1) from investigations of the Raman spectra at variable temperatures. The conformational stability, enthalpy difference, structural parameters, and fundamental vibrational frequencies, which have been determined experimentally, are compared to those obtained from ab initio Hartree-Fock calculations employing the 3-21G, 6-31 G^*, and 6-31 G^** basis sets.For part LVIII, seeStruct. Chem. 1991,2, 195.Taken in part from the thesis of M. J. Lee, which has been submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree, May 1991.     

Far-infrared spectrum,conformational stability,barriers to internal rotation,normal coordinate calculations,and vibrational assignment for chloroacetaldehyde

The far infrared spectrum [350 to 25 cm^–1] of gaseous chloroacetaldehyde, ClCH₂CHO, has been recorded at a resolution of 0.10 cm^–1. The first excited-state transition of the asymmetric torsion of the more stable near s-cis [chlorine atom s-cis to the aldehyde hydrogen atom] conformer has been observed at 26.9 cm^–1, with seven additional upper state transitions falling to higher frequency. Additionally, the fundamental torsional transition of the s-trans conformer has been observed at 58.9 cm^–1 with two excited states also falling to higher frequency. From these data, the asymmetric torsional potential coefficients have been determined to be:V ₁=414±11;V ₂ = 191±3;V ₃=–203±5;V ₄=44±1 andV ₆=–26±1 cm^–1. The s-cis to s-trans barrier is 500±5 cm^–1 (1.43±0.01 kcal mol^–1) with the s-cis conformer being more stable by 267±19 cm^–1 (0.76±0.05 kcal mol^–1) than the s-trans form. The Raman [4000 to 100 cm^–1] and infrared (4000 to 400 cm^–1] spectra of the gas have been recorded. Additionally, the Raman spectrum of the liquid has been recorded and qualitative depolarization values obtained. Complete vibrational assignments are proposed for both conformers based on band contours, depolarization values, and group frequencies. The assignments are supported by ab initio Hartree-Fock gradient calculations employing the 3–21G^* basis set to obtain the frequencies and the potential energy distributions for the normal vibrations for both rotamers. Additional ab initio calculations at the MP4/6-31G^* level have been carried out to determine the structural parameters for both conformers. The results are discussed and compared with the corresponding quantities obtained for some similar molecules.This contribution taken in part from the thesis of C. L. Tolley which will be submitted to the Department of Chemistry in partial fulfillment of the Ph.D. degree.     

Far infrared spectrum,conformational stability,barriers to internal rotation,vibrational assignment,and ab initio calculations of 2-chloro-3-fluoropropene

The far infrared spectrum (375 to 30 cm^–1) of gaseous 2-chloro-3-fluoropropene, CH₂=C(CH₂F)CI, has been recorded at a resolution of 0.10 cm^–1. The fundamental asymmetric torsional mode is observed at 117.5 cm^–1 with ten excited states falling to low frequency for thes-cis (fluorine atom eclipsing the double bond) conformer. For the higher energy gauche conformer, the asymmetric torsion is estimated to be at 94 cm^–1. From these data the asymmetric torsional potential function has been calculated. The potential function coefficients are calculated to be in cm^–1):V ₁=803±21,V ₂=–94±21,V ₃= 1025±10,V ₄=95±10, andV ₆=2±1, with an enthalpy difference between the more stables-cis and gauche conformera of 550±100 cm^–1 (1.57±0.29 kcal/mol). This function gives values of 1227±50cm^–1(3.51±0.14kcal/mol), 1266±200 cm^–1 (3.62±0.57 kcal/mol), and 665±100 cm^–1 (1.90±0.29 kcal/mol), for thes-cis to gauche, gauche to gauche, and gauche tos-cis barriers, respectively. From the relative intensities of the Raman lines of the gas at 652 cm^–1 (gauche) and 731 cm^–1 (s-cis) as a function temperature, the enthalpy difference is found to be 565±96 cm^–1 (1.62±0.27 kcal/mol). However, the more polar gauche conformer remains in the crystalline solid. The Raman spectrum of the gas has been recorded from 3500 to 70 cm^–1 and, utilizing these data and the previously reported infrared data, a complete vibrational analysis is proposed for both conformers. The conformational stability, barriers to internal rotation, fundamental vibrational frequencies, and structural parameters that have been determined experimentally are compared to those obtained from ab initio Hartree-Fock gradient calculations employing both the 3–21 G^* and 6–31G^* basis sets and to the corresponding quantities for some similar molecules.     

Hydrogenation of the silanone groups (≡Si-O)2Si=0. Experimental and quantum-chemical studies

The reactivity of bis(siloxy)silanone groups (Si-0)₂Si=O stabilized on a silica surface with respect to H₂ molecules was studied. The reaction was found to give the (Si-O)₂SiH(OH) groups. The rate constant for this process was determined. Its activation energy in the 300–580 K temperature range is 13.4±0.3 kcal mol^–1, and the enthalpy is 54±5 kcal mol^–1. The activation energy for the reverse reaction,viz., elimination of a hydrogen molecule, is equal to 65 kcal mol^–1. Quantum-chemical calculations of hydrogenation of F₂Si=O and (HO)₂Si=O, which are the simplest molecular models of the silanone groups, were performed. Data on the geometrical and electronic structures of transition states and on the effects of substituents at the silicon atom on the reactivity of the silanone groups in this process were obtained. The optical absorption band of the surface silanone groups was quantitatively characterized. Its maximum is located at 5.65±0.1 eV; the extinction coefficient at the maximum (220 nm) is (3±0.5) · 10^–18 cm² molec.^–1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1951–1958, August, 1996.     

Détermination colorimétrique de l'Iode sous forme de triiodure de Nitrone

Résumé Etudiant l'action mutuelle du nitron (Nt) et certains complexes halogènes on a obtenu le composé NtI₃. On a établi les propriétés, la composition et le mécanisme de la formation du composé. Ses propriétés ont servi de base à l'élaboration d'une méthode d'extraction et de détermination colorimétrique de microquantités d'iode. La méthode est basée sur l'oxydation de I^– en IO₃ ^–, réduction de ces derniers à l'aide de I^– en milieu acide et obtention de I₃ ^–, qu'on extrait sous forme de NtI₃ à l'aide de C₂H₄Cl₂ en presence de NtHSO₄. La méthode peut être mise à profit en présence de SO₄ ^2–, Cl^–, Br^– et NO₃ ^–.Cette méthode permet la détermination de 2 à 20g d'iode, dans 25 ml de solution, le coefficient des variations étant de ±3%. On s'est servi de cette méthode pour déterminer l'iode dans des eaux de sondage.

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Fluorimetric determination of iodine in the form of nitron triiodide

Summary The compound NtI₃ has been obtained by studying the mutual action of nitron (Nt) and certain halogenated complexes. Its properties have been established, also its composition and the mechanism of the formation of the compound. Its properties have served as the base for the elaboration of an extractive method for the colorimetric determination of microquantities of iodine. The method is based on the oxidation of I^– into IO₃ ^–, reduction of the latter through I^– in acidic surroundings and obtaining I₃ ^–, which is then extracted in the form of NtI₃ with the aid of C₂H₄Cl₂ in the presence of NtHSO₄. The method may be employed to advantage in the presence of SO₄ ^2–, Cl^–, Br^–, and NO₃ ^–. This method permits the determination of from 2 to 20g of iodine in 25 ml of solution, the coefficient of variation being ±3%. The procedure has been used to determine the iodine in boring waters.

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Zusammenfassung Bei der Einwirkung von Nitron (Nt) auf gewisse Halogenkomplexe wurde die Verbindung NtJ3 erhalten, deren Eigenschaften, Zusammensetzung und Bildungsweise untersucht wurde. Sie eignet sich für die Extraktion und kolorimetrische Bestimmung von Mikromengen Jod. Jodid wird zu Jodat oxydiert, dieses in saurer Lösung mit Jodid reduziert und das dabei entstehende J3^– als NtJ3 mit Dichloräthan in Gegenwart von NtHSO₄ extrahiert. Das Verfahren ist bei Anwesenheit von Sulfat, Chlorid, Bromid und Nitrat anwendbar und eignet sich zur Bestimmung von 2–20g Jod in 25 ml Lösung mit einem Variationskoeffizienten von ±3%. Es wurde für die Jodbestimmung in Brunnenwasser verwendet.

     

Synthesis,Spectral Properties,and Crystal Structure of {Methoxo[4-phenylbutane-2,4-dione(p-nitrobenzoyl) hydrazonato(2-)]oxovanadium(V)}

The hydrazino complex {methoxo[4-phenylbutane-2,4-dione(p-nitrobenzoyl)hydrazonato(2-)]oxovanadium(V)}, VO(p-NO₂bhbzac)OCH₃, (1), has been prepared by the direct reaction of bis(benzoylacetonato) oxovanadium(IV), VO(bza)₂, with p-NO₂-C₆H₄C(O)NHNH₂, p-NO₂bh, in CH₃OH. The resulting compound contains benzoylacetone-(p-NO₂)benzoyl hydrazone as tridentate Schiff base-type ligand and OCH₃ group as Lewis base, both ligated to vanadium. The crystals are orthorhombic, with Z = 8, space group Pbca, a = 11.699(5) Å, b = 14.035(5) Å, c = 22.564(5) Å, R1 = 0.0756 and wR2 = 0.1302. The crystal structure demonstrated the square-pyramidal geometry of the VO_oxo(ONO)O coordination sphere with the oxo ligand at the apical position. The electronic absorption spectra revealed a ligand-to-metal charge-transfer (LMCT) band in the near UV region at _max = 23,700 cm^–1 (B = 5640 dm³ mol^–1 cm^–1) in CH₃CN, _max = 23,420 cm^–1 (B = 5550 dm³ mol^–1 cm^–1) in DMSO, and _max near 26,950 (sh) cm^–1 (B = 10,550 dm³ mol^–1 cm^–1) in CH₂Cl₂. The FT-IR spectra of (1) show the characteristic strong (V = O) stretching vibration at 993 cm^–1 and support the view that the oxovanadium complex is pentacoordinated and monomeric.