Molecular structures and ESR spectra of copper(ii) complexes with 2-hydroxypropiophenone acyldihydrazones

The dinuclear copper(ii) complexes with 2-hydroxypropiophenone acyldihydrazones (H₄L) having the composition [Cu₂L·mPy], where the L ligand contains the polymethylene chain with different lengths (from two to five units), were synthesized and studied. The crystal and molecular structures of the 2-hydroxypropiophenone adipoylhydrazone complex [Cu₂L·4Py]·Py were established by X-ray diffraction analysis. Copper atoms are 8.212 distant from each other, and their nearest environment has the tetragonal pyramidal geometry. The ESR spectra of solutions of the complexes based on acyldihydrazones of succinic, glutaric, and adipic acids contain seven HFS lines with the constant 40·10^–4 cm^–1 from two equivalent copper atoms. The spectra were interpreted as a result of the spin-spin exchange interaction of two unpaired electrons. An increase in the polymethylene chain length to five units prevents exchange interactions. The ESR spectrum of the complex with acyldihydrazone of pimelic acid contains a signal of four HFS lines with a _Cu = 73.4·10^–4 cm^–1, which is typical of mononuclear copper(ii) complexes.     

ESR study of weak exchange interactions in binuclear copper(ii) complexes with acyldihydrazones of fluorinated β-diketones

A series of binuclear copper(ii) complexes with acyldihydrazones of aliphatic dicarboxylic acids (from malonic to adipic) and fluorinated -diketones (trifluoro- and hexafluoroacetylacetone) of composition Cu₂L·2Py (H₄L is acyldihydrazone) were studied by ESR spectroscopy. The ESR spectra of solutions of complexes with trifluoroacetylacetone acyldihydrazones have an isotropic signal with a seven-line hyperfine structure from two equivalent copper nuclei (g = 2.112, a _Cu = (39—40)·10^–4 cm^–1), which is indicative of weak exchange interactions between the paramagnetic centers due to spin density delocalization through a chain of the -bonds of the polymethylene bridge. On going to hexafluoroacetylacetone derivatives, the coupling is suppressed and the ESR spectra of solutions of such complexes show a signal with a four-line hyperfine structure (g = 2.121—2.131, a _Cu = (55—63)·10^–4 cm^–1) typical of mononuclear copper complexes.     

Synthesis and study of binuclear vanadyl complexes with acyldihydrazones of salicylaldehyde and dicarboxylic acids

The binuclear vanadyl(ii) complexes [(VO)₂·2Py·2EtOH]·mH₂O with acyldihydrazones of salicylaldehyde (H₄L) and dicarboxylic acids were synthesized and studied. In these complexes, two chelate vanadyl(ii) complexes with the tridentate bicyclic ligands are linked to each other by the polymethylene bridges —(CH₂) _n — of different lengths varying from one to four units. The ESR spectra of solutions of these complexes, unlike those of analogous copper(ii) complexes, have an isotropic signal with an eight-line hyperfine structure (g = 1.972, a _V = 93·10^–4 cm^–1) typical of monomeric vanadyl complexes, which indicates that no exchange interactions occur between the paramagnetic centers through the polymethylene chain.     

ESR study of weak exchange interactions in binuclear copper(ii) complexes with 2-hydroxyacetophenone acyldihydrazones

The binuclear copper(ii) complexes with 2-hydroxyacetophenone acyldihydrazones (H₄L) Cu₂L·2Py were studied by ESR spectroscopy. In these complexes, the coordination polyhedra are linked via the polymethylene chain containing from one to five units. In the complexes based on acyldihydrazones of malonic, succinic, glutaric, and adipic acids, weak spin-spin exchange interactions occur between the paramagnetic centers. An increase in the length of the polymethylene chain to five units hinders exchange interactions, and the ESR spectrum of the corresponding complex has a signal typical of monomeric copper(ii) complexes.     

ESR spectra of spacered copper(II) dimers of 5-bromo-2-hydroxyacetophenone acyldihydrazones based on aliphatic dicarboxylic acids

Binuclear copper(II) complexes with 5-bromo-2-hydroxyacetophenone acyldihydrazones (H₄L) with the composition [Cu₂L·nPy] where the coordination polyhedra are linked by polymethylene chains with different lengths (from one to five units) have been synthesized and studied. The ESR spectrum of a polycrystalline sample of a complex based on malonyldihydrazone contains a major signal (g = 2.11) together with a weak signal corresponding to the forbidden transition (ΔM _S = 2, g = 4.18). At room temperature, ESR spectra of solutions of complexes of acyldihydrazones based on malonic, succinic, glutaric, and adipic acids contain seven HFS lines from two equivalent copper nuclei. These lines result from weak spin-spin exchange interaction between two unpaired electrons with the constant (36–38)·10⁻⁴ cm⁻¹. An increase in the polymethylene chain length to five units prevents the exchange interactions, and the ESR spectrum of a complex of the acyldihydrazone based on pimelic acid contains a signal of four HFS lines (a _Cu = 69.5·10⁻⁴ cm⁻¹), which is common to the monomeric copper(II) compounds. In the parallel orientation, the ESR spectrum of a frozen solution of the complex of malonyldihydrazone contained the superposition of signals due to fine and hyperfine structures with similar constants (D _∥ = 0.0074 cm⁻¹, A _∥ = 0.0070 cm⁻¹, g _∥ = 2.089, g _⊥ = 2.053). __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1752–1757, August, 2005.     

Gamma radiolysis of Methyl Red solution and reaction induced by γ-irradiated NaCl in Methyl Red

The -radiolysis of Methyl Red solution in HCl medium at pH=2 has been studied along with energy transfer reaction brought about byF and hole centers of -irradiated NaCl. The G-values for degradation of the azo dye indicator by radiolysis and -irradiated salt were determined as 9·10^–1 and 4.8·10^–3, respectively. The kinetic rate constants (k) of degradation are evaluated as 2·10^–5 rad^–1 in the case of direct radiolysis, while for the irradiated salt it is 2·10^–7 rad^–1. The extent of degradation by direct -radiolysis is 100–200 times greater as compared to that by the -irradiated salt. The same mechanism is proposed for radiolysis as well as the reaction induced by -irradiated sodium chloride.     

The structure and EPR spectra of binuclear copper(II) complexes with acyldihydrazones of β-diketones

The synthesis and structure of binuclear copper(II) complexes with acyldihydrazones of some β-diketones are described. The molecular structure of the copper(II) complex [Cu₂L·4Py] with trifluoroacetylacetone succinyldihydrazone (H₄L) was determined by the single-crystal X-ray analysis. Central atoms are bridged by a chain of seven σ-bonds with a Cu...Cu distance of 8.750 Å. EPR spectra of copper(II) complexes with acyldihydrazones of trifluoroacetylacetone and lower dicarboxylic acids containing from one to four methylene groups in the aliphatic spacer show the seven-line HFS due to spin-spin coupling of unpaired electrons with the two equivalent copper nuclei (g = 2.110, a = (38.5–40.5)⊙10^?4 cm^?1). By extending polymethylene spacer, as well as by modifying starting β-diketone, an exchange interaction between paramagnetic centers is suppressed.     

EPR study of weak exchange interactions in binuclear copper(ii) complexes with salicylaldehyde acyldihydrazones

The binuclear Cu^II complexes with bis(salicylidene)hydrazones of dicarboxylic acids and their analogs (H₄L) of composition [Cu₂L·2Py] in which the coordination polyhedra are linked by a polymethylene chain containing from one to eight CH₂ units were studied by EPR spectroscopy. Weak antiferromagnetic spin-spin exchange interactions between two Cu^II atoms were found in the complexes based on hydrazones of malonic, succinic, glutaric, and adipic acids. These exchange interactions are manifested in the EPR spectra of liquid solutions as seven-line hyperfine signals from two equivalent Cu^II atoms with the hyperfine coupling constant a _Cu 40·10^–4 cm^–1. The exchange ceases as the length of the polymetylene chain increases to five-eight units and the EPR spectra show a four-line signal with a _Cu 80·10^–4 cm^–1 typical of mononuclear complexes.     

Spacered dinuclear copper(<Emphasis Type="SmallCaps">II</Emphasis>) complexes with acyldihydrazones of aliphatic dicarboxylic acids and 2-hydroxy-5-nitroacetophenone

Dinuclear copper(II) complexes with acyldihydrazones of 2-hydroxy-5-nitroacetophenone (H₄L) of the composition Cu₂(Py)_xL·mEtOH were synthesized and characterized. In these complexes, the coordination polyhedra of the copper atoms are linked to each other by a polymethylene chain of different lengths, from one to five monomer units. The structure of the [Cu₂L·4Mrf] complex (Mrf is morpholine) based on acyldihydrazone of malonic acid was established by X-ray diffraction. The copper(II) atoms in this complex are [4+1]-coordinated and are spaced by 6.94 Å. At room temperature, the signal in the ESR spectra of solutions of the complexes based on acyldihydrazones of malonic, succinic, glutaric, and adipic acids has a seven-line hyperfine structure with the constant of (35.3–38.8)·10⁻⁴ cm⁻¹ (g = 2.109–2.112) due to exchange interactions between unpaired electrons and two equivalent copper nuclei. An increase in the length of the polymethylene chain to five monomer units hinders exchange interactions, and the ESR signal of the complex based on acyldihydrazone of pimelic acid has a four-line hyperfine structure with a _Cu = 72.7·10⁻⁴ cm⁻¹ typical of mononuclear copper(II) complexes. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 229–234, February, 2007.     

Tail-end purification of americium from plutonium loading effluents using a mixture of octyl (phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide and tri-N-butyl phosphate

The tail-end purification of Am from Pu loading effluents in 7.5M HNO₃ containing 160 mg l^–1 Am and 1.2 mg l^–1 Pu has been carried out. With 0.2M CMPO+1.2M TBP in dodecane as the extractant and stripping by 0.04M HNO₃+0.05M NaNO₂, the Pu level is brought down to 31.2 g l^–1. When the acidity was reduced to 4.2M HNO₃, one contact with 20% TLA/dodecane and subsequent extraction by a mixture of CMPO and TBP and stripping with 0.04M HNO₃+0.05M NaNO₂ gave Am samples without any detectable amounts of Pu. The recovery of Am was 90% by the first procedure and 98% by the second one.     

Magnetic and spectral properties of the coligand isomer pair: Cu{N(CN)2}2(pyrazole)2 and Cu{pyrazole · N(CN)2}2

Summary New coligand isomers of composition Cu{N(CN)₂}₂(pz)₂ and Cu{pz · N(CN)₂}₂ (pz = pyrazole) were prepared and studied by measuring their magnetic susceptibilities up to 4.2K and by aid of their e.s.r., ligand field and i.r. spectra. The susceptibility data have been analysed with various models for the exchange-coupled copper(II) polymers. It is shown that the resultant exchange coupling is ferromagnetic for Cu{N(CN)₂}₂(pz)₂ (J 1.1 - 1.4 cm^–1) but antiferromagnetic for Cu{pz · N(CN)₂}₂ (J –0.4 cm^–1). A polymeric chain structure is proposed for Cu{N(CN)₂}₂(pz)₂ havingpseudo-octahedrally coordinated copper(II) and CN-bridging dicyanamide ligands. Its coligand isomer contains anionic chelate ligands, formed by nucleophilic addition between N(CN)₂ and pz in the copper(II) coordination sphere, and giving with this central atom a square-planar system. Definite, but slight axial interaction takes place between these structure units.     

Sol-Gel Derived Nanocomposites and Nanoporous Oxide Powders and Related Coatings for the Reversible Chemisorption of Hydrogen Sulfide

Two types of nanocomposites and nanoporous powders and related coatings were prepared by the sol-gel route. These silica-based materials contain dispersed reactive oxides, ZnO and ZnCr₂O₄, respectively. Experiments evidenced their ability of reversible chemisorption of H₂S as ZnS. Their attractive porous characteristics (small pore size 2–2.5 nm, high specific surface area 900–1100 m²· g^–1, high porosity 50–60%) are not significantly modified during the successive treatments of H₂S chemisorption and oxide regeneration. These preliminary results encourage to pursue this study which aims at the preparation of nanofilters for the desulfurization of gas mixtures.     

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.     

Spectrophotometric determination of iron at the p. p. m. level in sugar samples with 2-nitroso-5-dimethylaminophenol

Summary Ppm amounts of iron in sugar samples were determined spectrophotometrically with 2-nitroso-5-dimethylaminophenol (nitroso-DMAP). The iron(II) complex formed with nitroso-DMAP, is stable in aqueous solution at about pH 9. The method is simple, rapid, selective and very sensitive (molar absorptivity: 4.0×l0⁴l-mol^–1-cm^–1).

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Zusammenfassung Ppm-Mengen Eisen in Zuckerproben wurden spektrophotometrisch mit Hilfe von 2-Nitroso-5-dimethylaminophenol (Nitroso-DMAP) bestimmt. Der Eisen(II)komplex mit Nitroso-DMAP ist in wäßriger Lösung bei pH9 beständig. Das Verfahren ist einfach, rasch, selektiv und sehr empfindlich (molare Extinktion: 4,0·10⁴ l·Mol^–1·cm^–1).

     

Molecular spectra of nitroisoxazolinones

A study is made of IR and UV spectra of N-oxides of nitroisoxazolinones, and of derivatives of isoxazolidine and isoxazolizidine. Absorption bands are related to valence vibrations of N-O in the NO₂ group; in conjugated systems (in N-oxides of nitroisoxazolines) _s and _as are equal to 1310 and 1510 cm^–1, in nonconjugated systems (in nitroisoxazolidines) 1360 and 1560 cm^–1, respectively. Frequencies of N-O bond vibrations in N-oxides appear in the region 830–870 cm^–1, of the O-N-O fragment in isoxazolidines and isoxazolizidines in the 1010–1060 cm^–1 region. Measurements are made of total intensities of N-O valence vibrations in the NO₂ group in N-oxides of nitroisoxazolines and nitroisoxazolizidines, as well as of C=N valence vibrations in N-oxides of nitroisoxazolines.     

Kinetic and EPR studies on radical polymerization. Radical polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate

The polymerization of di-2[2-(2-methoxyethoxy)ethoxy]ethyl itaconate (1) with dimethyl 2,2-azobisisobutyrate (2) was studied, in benzene, kinetically and spectroscopically with the electron paramagnetic resonance (EPR) method. The polymerization rate (R _p) at 50°C is given by the equation:R _p=k[2]^0.48 [1]^2.4. The overall activation energy of polymerization was calculated to be 34 kJ·mol^–1. From an EPR study, the polymerization system was found to involve EPR-observable propagating polymer radicals of 1 under the actual polymerization conditions. Using the polymer radical concentration, the rate constants of propagation (k _p) and termination (k _t) were determined. With increasing monomer concentration,k _p(1.54.3 L·mol^–1·s^–1 at 50°C) increases andk _t (1.0·10⁴4.2·10⁴ L·mol^–1·s^–1 at 50°C) decreases, which seems responsible for the high dependence ofR _p on the monomer concentration. The activation energies of propagation and termination were calculated to be 11 kJ·mol^–1 and 84 kJ·mol^–1, respectively. For the copolymerization of 1(M ₁) and styrene (M ₂) at 50°C in benzene the following copolymerization parameters were found:r ₁=0.2,r ₂=0.53, Q₁=0.57, ande ₁=+0.7.     

Binuclear copper(II) complexes with acyldihydrazones of saturated carboxylic acids and pyruvic acid

Copper(II) binuclear complexes with acyldihydrazones of saturated carboxylic acids and pyruvic acid in which the coordination polyhedra are connected by polymethylene chains of different length (1 to 5 units) were synthesized and studied by chemical and thermogravimetric analysis, IR spectroscopy, and EPR. The structure of binuclear copper(II) complex with succinic acid acyldihydrazone [Cu₂L · 4Py] · 2Py was determined by X-ray diffraction. The crystals are monoclinic: a = 14.3795(6), b = 8.8736(4), c = 15.9147(7) Å, β = 101.062(3)°, space group P2₁/c, Z = 2. The number of independent reflections with I > 2σ(I) = 2804, R = 0.042, R _w = 0.087. The copper atoms are spaced by a chain of seven σ bonds at 8.922 Å. The coordination polyhedron can be described as a tetragonal pyramid highly distorted toward a trigonal bipyramid. The EPR spectra of solutions of complexes based on malonic, succinic, glutaric, and adipinic acids exhibit a poorly resolved signal of seven HFS lines with a constant of (26.3–27.0) × 10^?4 cm^?1, which attests to the presence of weak exchange interactions between paramagnetic centers. An increase in the length of the polymethylene spaur suppresses exchange interactions, and the EPR spectrum of the complex based on pimelic acid acyldihydrazone shows a signal of four HFS lines with a constant of 43.8 × 10^?4 cm^?1 typical of monomeric copper(II) complexes.     

Electronic and ESR spectroscopic study of thiocyanate-containing coordination compounds of titanium(III) in alcohol solutions

In an investigation of electronic and ESR spectra, it has been established that titanium(III) with the thiocyanate ion (in ethanol) forms distorted tetrahedral and octahedral complexes. The tetrahedral compounds, which are hydroxo complexes of titanium(III) that contain one hydroxyl group and three thiocyanate ions in the coordination sphere, give signals in the ESR spectra with g_o=1.960, A_o=15.0·10^–4 cm^–1 g=1.958, A ^Ti =26.4·10^–4cm^–1, g= 1.691, A^Ti=9.0·10^–4 cm^–1. In the ESR spectra of liquid solutions, additional splitting on the nitrogen atoms is manifested(A _o ^N =2.2·10^–4 cm^–1), which indicates bonding of thiocyanate ions through the nitrogen atom. The pseudo-octahedral complexes of titanium(III), containing from two to six thiocyanate ions in the coordination sphere, are characterized by d-d absorption bands in the 520–590 nm region; and at 77°K, they give anisotropic ESR signals. On the basis of the temperature dependences of the equilibrium constants for the reaction of conversion of the tetrahedral complexes to the octahedral complexes, and also the lifetimes of the tetrahedral complexes, values have been estimated for the heat of reaction (H=26.8 kJ/mole) and the entropy change (S=–1.66 kJ/mole·°K) of the equilibrium process, and also the activation energy for the reaction of titanium(III) thiocyanate formation (E=37 kJ/mole).Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 5, pp. 560–567, September–October, 1985.     

Spectral Hole-Burning in Femtosecond Laser-Irradiated Eu<Superscript>3+</Superscript>-Doped Aluminosilicate Glasses

We studied the persistent spectral hole-burning (PSHB) of the Eu³⁺-doped Al₂O₃-SiO₂ glasses, prepared by a sol–gel process, exposed to femtosecond laser pulses. The spectral holes were burned in the excitation spectra of the ⁷F₀⁵D₀ transition of Eu³⁺ ion. The depth and width of the burned holes were 15% and 2.5 cm^–1 fwhm at 7 K, respectively. The burned hole is stable up to room temperature. Fluorescence line narrowing spectra showed that Eu³⁺ ions were located in two different sites.     

Mechanisms of anion formation in O2, O2/Ar and O2/Ne clusters; the role of inelastic electron scattering

Measurements are reported on the formation of negative ions in O₂, O₂/Ar and O₂/Ne clusters aimed at establishing the mechanisms of anion formation and the role of inelastic electron scattering by the cluster constituents on negative ion formation in clusters. In the case of pure O₂ clusters the main anions we detected are of two types: O^–(O₂) _n0 and (O₂) _n ^1– . The yields of O^–(O₂) _n showed maxima at 6.3, 8.0 and 14.0 eV and the data suggest O^– as their precursor; the maxima at 8 and 14 eV are due to the production of O^– via symmetry forbidden dissociative attachment processes in O₂ at these energies which become allowed in clusters. The yields of (O₂) _n ^– showed a strong maximum at near-zero energy (0.5 eV) and also at 6.3, 8 and 14 eV. With the exception of the near-zero energy resonance, the (O₂) _n ^– anions at 6.3, 8 and 14 eV are attributed to nondissociative attachment of near-zero energy secondary electrons to O₂ clusters. The slow secondary electrons result predominantly from scattering via the O ₂ ^– negative ion states of incident electrons with energies in their respective regions. Similar results were obtained for the mixed O₂/rare gas clusters except that now a feeble and distinctly structured contribution in the yields of O^–(O₂) _n , (O₂) _n ^– (and Ar(O₂) _n ^– ) was observed at energies >10 eV. These anions are believed to have the lowest negative ion states of Ar*^– (Ne*^–) as their precursors.