Thermal decomposition of rare earth element suberates in air atmosphere

The condition of thermal decomposition of La, Ce(III), Pr(III), Nd, Sm, Eu(III), Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu suberates were studied. The suberates of Ce(III), Sm, Eu(III), Ho, Tm, Yb and Lu heated lose crystallization water. Anhydrous Sm and Eu(III) suberates decompose to oxides with intermediate formation Ln₂O₂CO₃, whereas suberates of other lanthanides decompose directly to oxides. Suberates of La, Pr(III), Nd, Gd, Tb, Dy and Er lose some water molecules and then decompose directly to oxides. Only La complex decomposes to La₂O₃ via the intermediate formation La₂O₂CO₃.

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Zusammenfassung Es wurden die UmstÄnde der thermischen Zersetzung von La-, Ce(III)-, Pr(III)-, Nd-, Sm-, Eu(III)-, Gd-, Tb-, Dy-, Ho-, Er-, Tm-, Yb- und Lu-suberat untersucht. Bei Erhitzen verlieren Ce(III)-, Sm-, Eu(III)-, Ho-, Tm-, Yb- und Lu-suberat Kristallwasser. Wasserfreies Sm-bzw. Eu(III)-suberat zersetzt sich über das Zwischenprodukt der Zusammensetzung Ln₂O₂CO₃ zum Oxid, wÄhrend sich die Suberate der anderen Lanthanoide direkt zu den Oxiden zersetzen. La-, Pr(III)-, Nd-, Gd-, Tb-, Dy- und Er-suberat geben einige Moleküle Kristallwasser ab und zersetzen sich dann direkt zu den Oxiden. Nur der Lanthankomplex zersetzt sich zu La₂O₃ über das Zwischenprodukt La₂O₂CO₃.

     

Borderline of hydrogen bonding of silanols

Two new silanols bearing very bulky silyl groups, (i-Pr₃ Si)₃SiOH and (t − BuMe₂Si)₃SiOH were prepared by peracidoxidation of their respective silanes. The X − ray crystallographic analysis revealed that (t − BuMe₂Si)₃ SiOH forms a dimeric structure with hydrogen bonding, while (i − Pr₃ Si)₃ SiOH exists as a monomer in the crystal. The effects of the size of the substituents as well as the reactivity of these silanols are discussed.     

Unusual hydrogen bonding in L‐cysteine hydrogen fluoride

L‐Cysteine hydrogen fluoride, or bis(L‐cysteinium) difluoride–L‐cysteine–hydrogen fluoride (1/1/1), 2C₃H₈NO₂S⁺·2F⁻·C₃H₇NO₂S·HF or L‐Cys⁺(L‐Cys...L‐Cys⁺)F⁻(F⁻...H—F), provides the first example of a structure with cations of the `triglycine sulfate' type, i.e.A⁺(A...A⁺) (where A and A⁺ are the zwitterionic and cationic states of an amino acid, respectively), without a doubly charged counter‐ion. The salt crystallizes in the monoclinic system with the space group P2₁. The dimeric (L‐Cys...L‐Cys⁺) cation and the dimeric (F⁻...H—F) anion are formed via strong O—H...O or F—H...F hydrogen bonds, respectively, with very short O...O [2.4438 (19) Å] and F...F distances [2.2676 (17) Å]. The F...F distance is significantly shorter than in solid hydrogen fluoride. Additionally, there is another very short hydrogen bond, of O—H...F type, formed by a L‐cysteinium cation and a fluoride ion. The corresponding O...F distance of 2.3412 (19) Å seems to be the shortest among O—H...F and F—H...O hydrogen bonds known to date. The single‐crystal X‐ray diffraction study was complemented by IR spectroscopy. Of special interest was the spectral region of vibrations related to the above‐mentioned hydrogen bonds.     

Characterization of an argon-hydrogen microwave discharge used as an atomic hydrogen source. Effect of hydrogen dilution on the atomic hydrogen production

This work is devoted to the study of an argon-hydrogen microwave plasma used as an atomic hydrogen source. Our attention has focused on the effect of the hydrogen dilution in argon on atomic hydrogen production. Diagnostics are performed either in the discharge or in the post-discharge using emission spectroscopy (actinometry) and mass spectrometry. The agreement between actinometry and mass spectrometry diagnostics proves that actinometry on the Ha(656.3 nm) and Hβ(486.1 nm) hydrogen Balmer lines can be used to measure the relative atomic hydrogen density within the microwave discharge. Results show that the atomic hydrogen density is maximum for a gas mixture corresponding to the partial pressure ratioP _{H 2}/P _Ar range between 1.5 and 2. The variation of atomic hydrogen density can be explained by a change of the dominant reactive mechanisms. At a low hydrogen partial pressure the dominant processes are the charge transfers with recombinations between Ar⁺ and H₂ which lead to ArH⁺ and H ₂ ⁺ ion formation. Both ions are dissociated in dissociative electron attachment processes. At a low argon partial pressure the electron temperature and the electron density decrease with increasing partial pressure ratio. The dominant mechanisms become direct reactions between charged particles (e, H⁺, H ₂ ⁺ , and H ₃ ⁺ ) or excited species H(n=2) with H₂ producing H atoms.     

Triethyl­ammonium hydrogen fumarate

In crystals of the title compound, the hydrogen fumarate anions form one‐dimensional chains through an O—H?O hydrogen bonding along the c and (a+b)/2 directions. There are three sites of the hydrogen fumarate, two of which have an inversion centre.     

Betaine betainium hydrogen oxalate

The title compound, C₅H₁₂NO₂⁺·C₂HO₄⁻·C₅H₁₁NO₂ or HC₂O₄⁻·(HBET·BET)⁺ [BET is tri­methyl­glycine (betaine); IUPAC name: 1-carboxy-N,N,N-tri­methyl­methanaminium hydro­xide inner salt], contains pairs of betaine mol­ecules bridged by an H atom, forming dimers linked by a strong hydrogen bond. The hydrogen oxalate anions have a rather unusual star conformation, with an internal torsion angle of 70.1 (4)°. The betaine–betainium dimers are anchored between two zigzag chains of hydrogen oxalate mol­ecules hydrogen bonded head-to-tail running parallel to the b axis. An extended network of C—H⃛O interactions links the anionic chains to the cationic dimers.     

Variation of the polarizability of the hydrogen molecule ion and the hydrogen molecule with internuclear separation

The variation of the polarizability of H and H₂ with internuclear separation R = 1.6 – R = 2.4 a.u. for H and R = 1.0 – R = 2.0 a.u. for H₂ is determined using a variational method suggested by Das and Bersohn. From these data, values of 〈α〉_0,J for which nuclear motion due to zero point vibration and centrifugal stretching is taken into account, are calculated at 300°K. The relative percent increases of the motion averaged values compared to the equilibrium values are as follows: 10.50% for H and 6.52% for H₂.     

The expansion of hydrogen states in Gaussian orbitals

The convergence properties of Gaussian orbitals are studied by considering a very simple system, the hydrogen atom. We have variationally optimized even-tempered basis sets containing up to 60 s functions for the ground state and the first excited S state of the hydrogen atom, to an accuracy of 10^–15E_h. In addition, we have freely optimized the exponents in basis sets containing up to 12 Gaussians. We have studied the convergence of the total energy, the kinetic energy, the extent of the atom as measured by r², and the Fermi-contact interaction at the nucleus in these basis sets as well as in basis sets augmented with additional diffuse or steep functions.     

Infrared study of hydrogen bonds involving N-heterocyclic bases and phenols

The hydrogen bond complexes between phenols and N-heteroaromatic bases 2,4,6-tri(2-pyridyl)-1,3,5-triazine, 2,2′,2′-terpyridine, quinoxaline, pyrido[2,3-b]pyrazine, pyzazino [2,3f]quinoxaline and 5-nitrozphenanthroline are investigated by infrared spectroscopy in 1,2-dichloroethane. The stability constants of the complexes involving N-heteroaromatic bases characterized by tow vicinal nitrogen atoms having lone pairs pointing to each other are higher than predicted from their basicity. Possible differences between protonation and hydrogen bond formation are discussed. Nheteroaromatic bases such as tri(2-pyridyl)-1,3,5-triazine or phenanthrolines cannot be considered as proton sponges but their behaviour is intermediate between that of the classical heteroaromatic bases and the proton sponges.     

Covalent nature of the hydrogen bond

Conclusions The main conclusion derived from this work is that the H bond in all three FHF^–, FHFH, and HFHFH⁺ systems is a three-centered, two-electron, covalent chemical bond formed at the expense of 2a _1g (2a ₁) MO bonding. The 1a _1g MO bonding has little effect on H-bond stabilization. Thus the H bond is a one-orbital chemical bond with its formation corresponding, to that of a three-centered MO, as distinguished from molecules bonded by a two-centered MO (e.g., F₂ or HOOH [41]; hence the H bond is much weaker. The uniqueness of the H bond lies in its being the weakest covalent bond. It is precisely the covalent nature of the H bond that gives it its characteristic properties, i.e., saturability and strict compliance to structural requirements. In addition, the low dissociation barrier makes it easy to control the H bond under mild conditions, which is very important in biological systems.Translated from Zhurnal Strukturnoi Khimii, Vol. 26, No. 2, pp. 13–21, March–April, 1985.     

Valence bond functions for the hydrogen molecule

Valence bond wavefunctions were constructed for H₂. Use of Slater exponents resulted in very slow convergence to the ground state energy. Convergence was improved by optimizing exponents which were found to increase as the principal quantum number n. However, this gave problems of linear dependence since optimum orbitals were strikingly similar for all n. The best function without angular correlation contained 27 terms constructed from 1s, 3s, 2p ₀, 3d ₀, 4f ₀, and 5g ₀ orbitals and gave an energy of –1.1594a.u. The best function with angular correlation gave E=-1.1656 a.u.

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Zusammenfassung Für das H₂-Molekül werden Wellenfunktionen nach der Valenzstrukturmethode konstruiert. Die Benutzung von Exponenten nach Slater führt zu einer sehr langsamen Konvergenz zur Grundzustandsenergie. Die Konvergenz wurde durch Optimierung der Exponenten verbessert, wobei diese mit der Hauptquantenzahl ansteigen. Dabei ergab sich jedoch das Problem linearer Abhängigkeit der Funktionen, da die optimalen Orbitale sehr ähnlich für alle n waren. Die beste Funktion ohne Winkelkorrelation enthielt 27 Terme, die aus den Orbitalen 1s, 3s, 2p ₀, 3d ₀, 4f ₀ und 5g ₀ konstruiert waren, und ergab eine Energie von –1,1594A.E. Die beste Funktion mit Winkelkorrelation ergab E=–1,1656 A.E.

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Résumé Des fonctions d'onde de liaison de valence sont construites pour H₂. L'emploi d'exposants de Slater entraîne une très faible convergence vers l'énergie de l'état fondamental. La convergence a été améliorée par optimisation des exposants qui croissent comme le nombre quantique principal n. Cependant, ceci crée des problèmes de dépendance linéaire car les orbitales optimales sont étonnement similaires pour tous les n. La meilleure fonction sans corrélation angulaire contient 27 termes construits à partir d'orbitales 1s, 3s, 2p ₀,3d ₀,4f ₀ et 5g ₀ et donne une énergie de –1,1594 u.a. La meilleure fonction avec corrélation angulaire donne E= –1,1656 u.a.

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Presented in part at the Symposium on Molecular Structure and Spectroscopy, The Ohio State University, Sept., 1968.

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N.I.H. Predoctoral Fellow 1964–1967.     

p-character and the polarizability of molecular hydrogen

The polarizability of molecular hydrogen has been calculated over a range of internuclear separations by Hartree-Fock perturbation theory, both coupled and uncoupled, using Gaussian functions as basis set. It is shown that a relatively simple function having the proper admixture of s and p character can yield polarizabilities comparable in accuracy with those obtained from highly sophisticated wave-functions.

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Zusammenfassung Die Polarisierbarkeit des Wasserstoffmoleküls wurde für einen Bereich von Kernabständen mit Hilfe der gekoppelten als auch der entkoppelten Hartree-Fock-Störungstheorie mit einer Basis von Gauss-Funktionen berechnet. Es wird gezeigt, daß eine relativ einfache Funktion mit der geeigneten Beimischung von s- und p-Charakter Polarisierbarkeiten ergibt, deren Genauigkeit solchen aus Rechnungen mit sehr komplizierten Wellenfunktionen vergleichbar ist.

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Résumé Calcul de la polarisabilité de l'hydrogène moléculaire pour un éventail de distances internucléaires par la théorie des perturbations Hartree-Fock, couplée et non couplée, dans une base de fonctions gaussiennes. Une fonction relativement simple présentant un mélange convenable de caractère s et p fournit des polarisabilités, comparables au point de vue précision avec celles obtenues à partir de fonctions d'ondes très élaborées.

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Supported by the National Science Foundation; Grant No. GP-8359.     

Excited electronic states of a hydrogen bond: Bifluoride ion

We report here a summary of a limited CI calculation carried out on the C_∞v and D_∞h electronically excited states of bifluoride ion. This species is interesting as the prototype of a hydrogen-bonded system. It is determined that the lowest-lying excited states of the system are dissociative and/or autoionizing.     

Steam-reforming of ethanol for hydrogen production

Production of hydrogen by steam-reforming of ethanol has been performed using different catalytic systems. The present review focuses on various catalyst systems used for this purpose. The activity of catalysts depends on several factors such as the nature of the active metal catalyst and the catalyst support, the precursor used, the method adopted for catalyst preparation, and the presence of promoters as well as reaction conditions like the water-to-ethanol molar ratio, temperature, and space velocity. Among the active metals used to date for hydrogen production from ethanol, promoted-Ni is found to be a suitable choice in terms of the activity of the resulting catalyst. Cu is the most commonly used promoter with nickel-based catalysts to overcome the inactivity of nickel in the water-gas shift reaction. γ-Al₂O₃ support has been preferred by many researchers because of its ability to withstand reaction conditions. However, γ-Al₂O₃, being acidic, possesses the disadvantage of favouring ethanol dehydration to ethylene which is considered to be a source of carbon deposit found on the catalyst. To overcome this difficulty and to obtain the long-term catalyst stability, basic oxide supports such as CeO₂, MgO, La₂O₃, etc. are mixed with alumina which neutralises the acidic sites. Most of the catalysts which can provide higher ethanol conversion and hydrogen selectivity were prepared by a combination of impregnation method and sol-gel method. High temperature and high water-to-ethanol molar ratio are two important factors in increasing the ethanol conversion and hydrogen selectivity, whereas an increase in pressure can adversely affect hydrogen production.     

Diffusion Monte Carlo study of correlation in the hydrogen molecule

The diffusion Monte Carlo (DMC) method shows that correlation in H₂ produces a set of three spatial changes: (i) an enhancement in the electron density distribution n( r ) in the left and right anti‐binding regions that include separately the immediate vicinity of each of the two nuclei, (ii) a reduction in n( r ) in the binding region intervening between the two nuclei as a counterbalance, and (iii) a concomitant increase in the equilibrium internuclear separation. It is stressed that the correlation energy E^c (= T^c + V^c) for diatomic molecules be defined by the difference in the total energy between the exact and the Hartree–Fock (HF) variational calculations that are performed at individually optimized internuclear separations. It is this definition that makes it possible to involve a significant contribution from a correlation‐induced change in the equilibrium internuclear separation as part of the correlation energy and to relate (i) and (ii) to (iii) in consistency with the electrostatic theorem. The present calculations fulfill the virial theorem to an accuracy of ?V/T = 2.00 for DMC and ?V^HF/T^HF = 2.000 for HF. The present correlation energy E^c = ?0.0408 hartree is not only in good agreement with the most accurate value previously reported, but also can be analyzed into all its components in accordance with the correlational virial theorem 2T^c + V^c = 0. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007     

Long-lived metastable anions of hydrogen halides

We search for narrow resonances in cross-sections for electron collisions with HCl, DCl, HBr and DBr molecules, calculated with the nonlocal resonance model. Narrow resonances corresponding to long-lived metastable states of anionic molecules are indeed found in both elastic and vibrational excitation cross-sections. The largest lifetime τ = 0.11 ms is predicted for HBr⁻ with rotational quantum number J = 20. For HCl we find maximum τ = 0.6 ns for J = 22 and τ = 0.6 μs for J = 33 in DCl. A surprising isotope effect is found for DBr, where the largest lifetime is τ = 1.5μs, i.e., much smaller than for HBr.     

Electronic structure and the hydrogen-shift isomerization of hydrogen nitryl HNO2

Summary Electronic structure of hydrogen nitryl HNO₂, a yet not identified entity, and the path of its possible isomerization totrans-HONO have been investigated byab initio SCF and MRD-CI computations using the 6-31G** basis set. HNO₂ isC _2v -symmetric and its ground state (¹ A ₁) is less stable thantrans-HONO by 66 kJ/mol (with the SCF vibrational zero-point energy correction). The lowest two excited singlet states (¹ A ₂ and¹ B ₁) are nearly degenerate, their vertical excitation energies being predicted to be 4.8 eV. The isomerization path is traced by the CASSCF procedure and the activation barrier height is evaluated by the CI treatment. HNO₂ in its ground state isomerizes totrans-HONO by maintaining the planar (C _s-symmetric) structure. The activation energy is calculated to be 171 kJ/mol, which is clearly lower than the calculated H-N bond energy (253 kJ/mol). The transition state seems to be more adequately described as an interacting system of proton and the nitrite anion rather than as a pair of two fragment radicals.     

Two-dimensional model of intramolecular hydrogen bond

One- and two-dimensional vibrational problems were solved to determine the states of H and D in the intramolecular hydrogen bond of malonic dialdehyde. Within the one-dimensional approach the model potential (barrier height 51 kJ/mol) satisfied with the IR and microwave spectroscopy data. For the two-dimensional problem an approach to evaluation of eigenvalues with high accuracy based on the Ritz method was developed. Within the two-dimensional approximation the barrier height was taken to be 57 kJ/mol. An introduction of the second dimension was found to give rise to the vibrational non-adiabatic effects.