Magnetic properties of group VIB hexacarbonyls. Suggestion of a new diamagnetic susceptibility standard

Summary Careful measurements of the magnetic susceptibilities of group VI B metal hexacarbonyls show an ideal diamagnetic behaviour. The properties of W(CO)₆, together with the relatively low price, lead to the suggestion of W(CO)₆ as a new calibration standard for the diamagnetic region.

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Magnetische Eigenschaften von Hexacarbonylen der Gruppe VI B. Vorschlag zu einem neuen diamagnetischen Suszeptibilitätsstandard

Zusammenfassung Sorgfältige Messungen der magnetischen Suszeptibilität der Metallhexacarbonyle der Gruppe VI B zeigen deren ideal diamagnetisches Verhalten. Die physikalischen Eigenschaften des W(CO)₆, zusammen mit dem relativ niedrigen Preis, prädestinieren es als diamagnetischen Eichstandard.

     

Spektroskopische Untersuchungen und Phasenbeziehungen im System Li2O−Al2O3−Cr2O3

Zusammenfassung Aus Li₂CO₃ und (Al_1–x Cr _x )₂O₃ wurde durch Festkörperreaktionen die Mischkristallreihe LiAl_1–x Cr _x O₂ hergestellt. Die thermische Stabilität der mikrokristallinen Substanzen (-NaFeO₂-Typ, Raumgruppe R3m) wurde röntgenographisch verfolgt. Die diffusen Reflexionsspektren (12 bis 30 kK, 25°C) wurden mit dem Modell der erweiterten Kristallfeldtheorie ausgewertet. Die durch Multiphononen-Struktur charakterisierten spin-erlaubten Banden ergeben für kubische MikrosymmetrieDq- undRacah-B-Werte, die im Gegensatz zur Rubinreihe nur wenig von Cr-Gehalt abhängen.Dq beruht zum Teil auf dem Einfluß von zweitnächsten Li⁺-Nachbarn, wodurch die effektive Ladung der Sauerstoff-Liganden in der Bindung größer ist. Die breite spin-verbotene Bande bei 15 kK deutet auf eine Magnon-Satellitenstruktur durch antiferromagnetische Ordnung hin.

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Optical studies and phase relations in the system Li₂O–Al₂O₃–Cr₂O₃

The series LiAl_1–x Cr _x O₂ was prepared by solid state reactions with Li₂CO₃ and (Al_1–x Cr _x )₂O₃. The thermal stability of the microcrystalline samples (-NaFeO₂ type, space group R3m) was controlled by X-ray methods. The diffuse reflectance spectra at 25 °C in the region from 12 to 30 kK were analyzed by the extended crystal field theory. From the spin-allowed peaks characterized by a multiphonon structureDq-andRacah-B-values were obtained for cubic site symmetry (neglecting trigonal distortions and spin-orbit effects) that are only slightly dependent on the Cr-content, in contrast to the ruby series.Dq is partly due to the influence of the secondnearest Li⁺-neighbours leading to a greater effective charge of the oxygen ligands in the bond. The broad spin-forbidden peak at 15 kK points to a magnon satellite structure caused by antiferromagnetic ordering.

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Spektroskopische und magnetische Untersuchungen an einer neuen Nickel(II)—Azido-Komplexverbindung

Zusammenfassung Die elektronischen diffusen Reflexionsspektren bei Raumtemp. zwischen 7,5 und 28 kK und die magnetischen Susceptibilitäten bei 77°, 195° und 292° K wurden an einem erstmals dargestellten komplexen Nickel-Azid der Zusammensetzung K₄Ni(N₃)₆ gemessen. Die Analyse des Absorptionsspektrums auf ligandenfeldtheoretischer Grundlage zeigt eine oktaedrische N₃ ^–-Umgebung des Ni²⁺. Aus der Rechnung ergeben sich der Kristallfeldparameter zu 8,3 kK und dieRacah-ParameterB zu 0,76 kK undC zu 3,17 kK. Das gegenüber dem Nur-Spin-Wert vergrößerte effektive magnetische Moment ist durch die Beimengung von Bahnmomentanteilen des angeregten³T₂-Zustandes zum³A₂-Grundterm des Ni via Spin—Bahn-Kopplung bedingt. Der große Wert für und die gleichzeitige starke Reduktion derRacah-Parameter sowie der Spin—Bahn-Kopplungskonstanten weisen auf eine Elektronendelokalisierung im Zentralion und Polarisationseffekte im Liganden hin. Dadurch wird die Überlappung erhöht und der kovalente Bindungsanteil im [Ni(N₃)₆]^4–-Molekül verursacht, der wesentlich größer ist als im [NiF₆]^4–- und [Ni(H₂O)₆]²⁺-Molekül.

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The electronic diffuse reflectance spectra at ambient temperature between 7,5 and 28 kK of a complex nickel azide prepared for the first time and having the composition K₄Ni(N₃)₆ have been measured together with values of the magnetic susceptibility at 77°, 195° and 292° K. By ligand field analysis of the spectrum an octahedral N₃ ^–-environment around the Ni²⁺ was found. From the calculation the cubic crystal field parameter was determined to be 8,3 kK and the Racah parameters B=0,76 kK and C=3,17 kK. The effective magnetic moment was found to be larger than the spin-only value because of an orbital contribution of the excited³T₂ state to the³A₂ ground term of Ni²⁺ via spin-orbit coupling. The large crystal field splitting and the simultaneous large reduction of both the Racah parameters and the spin-orbit coupling constant are pointing at some delocalization among the d-electrons of the central ion and polarization effects within the ligands. Both effects are favorable for increasing overlapping and covalency within the [Ni(N₃)₆]^4–-molecule, the latter effect being much larger in the azide than for instance in the [NiF₆]^4–- and [Ni(H₂O)₆]²⁺-molecule.

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Electronic excitations during grazing scattering of hydrogen atoms on KI(001) and LiF(001) surfaces

The energy loss of hydrogen atoms with energies of 400 eV and 1 keV is studied in coincidence with the number of emitted electrons during grazing scattering from atomically clean and flat KI(001) and LiF(001) surfaces. The energy loss spectra for specific numbers of emitted electrons are analyzed in terms of a binary interaction model based on the formation of transient negative ions via local capture of valence band electrons from anion sites. Based on computer simulations we derive for this interaction scenario probabilities for the production of surface excitons, for electron loss to the conduction band of KI, for emission of electrons, and for formation of negative hydrogen ions. The pronounced differences of data obtained for the two surfaces are attributed to the different electronic structures of KI and LiF.     

14.5GHz紧凑型、低成本、全永磁ECR离子源

A compact 14.5GHz electron cyclotron resonance (ECR) ion source for the production of slow, multiply charged ions has been constructed,with the plasma-confining magnetic field produced exclusively by permanent magnets.Microwave power of up to 175W in the frequency range from 12.75 to 14.SGHz is transmitted from ground potential via a PTFE window into the water-cooled plasma chamber which can be equipped with an aluminum liner.The waveguide coupling system serves also as biased electrode,and two remotely-controlled gas inlet valves connected via an insulating break permit plasma operation in the gas- mixing mode.A triode extraction system sustains ion acceleration voltages between 1kV and 10kV.The ECR ion source is fully computer-controlled and can be remotely operated from any desired location via Ethernet.     

Molecular symmetry with quaternions

A new and relatively simple version of the quaternion calculus is offered which is especially suitable for applications in molecular symmetry and structure. After introducing the real quaternion algebra and its classical matrix representation in the group SO(4) the relations with vectors in 3-space and the connection with the rotation group SO(3) through automorphism properties of the algebra are discussed. The correlation of the unit quaternions with both the Cayley-Klein and the Euler parameters through the group SU(2) is presented. Besides rotations the extension of quaternions to other important symmetry operations, reflections and the spatial inversion, is given. Finally, the power of the quaternion calculus for molecular symmetry problems is revealed by treating some examples applied to icosahedral symmetry.     

Investigation of phase separation in Nd3+ doped ternary sodium borosilicate glasses by optical spectroscopy

Two glasses doped with 1 mol% Nd2O3 and batch compositions inside the miscibility gap of the ternary Na2O-B2O3-SiO2 system were prepared by rapid quenching of the 1,400 degrees C melts. Phase separation was induced by heat-treatment at 600 degrees C for different exposure times and monitored qualitatively by an observation of Rayleigh scattering. The 4I(9/2-->P(1/2) transition of Nd3+ around 23300 cm(-1) recorded for the quenched samples without heat-treatment was used to demonstrate that submicroscopic phase separation in the doped glasses occurs instantaneously upon quenching. The effect of the Nd3+ concentration on this submicroscopic phase separation was investigated.