Ueber die in der Milch enthaltenen Eiweissk?rper

Ohne Zusammenfassung     

Freie Mischungsenthalpie der Mischung von 1,2-Dichloräthan mit Cyclohexan

Zusammenfassung Totaldampfdrucke des Systems 1,2-Dichloräthan + Cyclohexan wurden bei 13°, 20° und 32° C über den gesamten Konzentrationsbereich gemessen. Für Cyclohexan-reiche Mischungen des Systems wurde ferner die Schmelzkurve bestimmt. Aus diesen Meßgrößen wurde die zusätzliche freie Mischungsenthalpie G ^E des Systems für verschiedene Temperaturen berechnet. Bei 20°C beträgt G ^E für die äquimolare Mischung 773 J/mol. Ein Vergleich mit Literaturangaben über die Mischungswärme (H=1611 J/mol für äquimolare Mischung bei 20°C) ergibt, daß die zusätzliche Mischungsentropie S ^E des Systems stark positiv ist. Eine Interpretation der Ergebnisse wird in einer anderen Arbeit gegeben, wo auch Ergebnisse an anderen Dihalogenäthan + Kohlenwassersoff-Systemen berücksichtigt werden.

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Free enthalpy of mixing for the system 1,2-dichloroethne-cyclohexane

Total vapour pressures of the system 1,2-dichloroethane + cyclohexane were measured at 13°, 20° and 32°C over the total concentration interval. For mixtures rich in cyclohexane the

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Mit 5 Abbildungen     

On the ultraviolet photodissociation of H(2)Te

The photodissociation of H(2)Te through excitation in the first absorption band is investigated by means of multireference spin-orbit configuration interaction (CI) calculations. Bending potentials for low-lying electronic states of H(2)Te are obtained in C(2v) symmetry for Te-H distances fixed at the ground state equilibrium value of 3.14a(0), as well as for the minimum energy path constrained to R(1)=R(2). Asymmetric cuts of potential energy surfaces for excited states (at R(1)=3.14a(0) and theta;=90.3 degrees ) are obtained for the first time. It is shown that vibrational structure in the 380-400 nm region of the long wavelength absorption tail is due to transitions to 3A('), which has a shallow minimum at large HTe-H separations. Transitions to this state are polarized in the molecular plane, and this state converges to the excited TeH((2)Pi(1/2))+H((2)S) limit. These theoretical data are in accord with the selectivity toward TeH((2)Pi(1/2)) relative to TeH((2)Pi(3/2)) that has been found experimentally for 355 nm H(2)Te photodissociation. The calculated 3A(')<--XA(') transition dipole moment increases rapidly with HTe-H distance; this explains the observation of 3A(') vibrational structure for low vibrational levels, despite unfavorable Franck-Condon factors. According to the calculated vertical energies and transition moment data, the maximum in the first absorption band at approximately 245 nm is caused by excitation to 4A("), which has predominantly 2(1)A(") ((1)B(1) in C(2v) symmetry) character.     

GRECP/MRD‐CI calculations on the Hg atom and HgH molecule

Multireference single‐ and double‐excitation configuration interaction (MRD‐CI) calculations of transition energies for the Hg atom and spectroscopic constants for the HgH molecule are carried out with the generalized relativistic effective core potential (GRECP) method. A new selection criterium for the reference configurations is discussed. The calculated spectroscopic constants are compared with experimental data and results of calculations of other groups. Improvement of accuracy is mainly observed for bond lengths from the GRECP/MRD‐CI calculations (without applying the T = 0 correction) with respect to the results of other groups. Analysis of the quality of the approximations employed is carried out. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002     

Theoretical study of the CH2 + O photodissociation of formaldehyde adsorbed on the Ag(111) surface

Configuration interaction calculations of the ground and excited states of the H2CO molecule adsorbed on the Ag(111) surface have been carried out to study the photoinduced dissociation process leading to polymerization of formaldehyde. The metal-adsorbate system has been described by the embedded cluster and multireference configuration interaction methods. The pi electron-attachment H2CO- and n-pi* internally excited H2CO* states have been considered as possible intermediates. The calculations have shown that H2CO* is only very weakly bound on Ag(111), and thus that the dissociation of adsorbed formaldehyde due to internal excitation is unlikely. By contrast, the H2CO- anion is strongly bound to Ag(111) and gains additional vibrational energy along the C-O stretch coordinate via Franck-Condon excitation from the neutral molecule. Computed energy variations of adsorbed H2CO and H2CO- at different key geometries along the pathway for C-O bond cleavage make evident, however, that complete dissociation is very difficult to attain on the potential energy surface of either of these states. Instead, reneutralization of the vibrationally excited anion by electron transfer back to the substrate is the most promising means of breaking the C-O bond, with subsequent formation of the coadsorbed O and CH2 fragments. Furthermore, it has been demonstrated that the most stable state for both dissociation fragments on Ag(111) is a closed-shell singlet, with binding energies relative to the gas-phase products of approximately 3.2 and approximately 1.3 eV for O and CH2, respectively. Further details of the reaction mechanism for the photoinduced C-O bond cleavage of H2CO on the Ag(111) surface are also given.     

Positron binding energies for alkali hydrides

Ab initio multireference single- and double-excitation configuration interaction (MRD-CI) calculations are carried out to study the interactions of positrons with the members of the alkali hydride class of molecules. A new computer program has been constructed for this purpose that makes use of the Table-Direct-CI method for construction of the required Hamiltonian matrixes and electronic/positronic wave functions. The calculations indicate that the binding energy (positron affinity PA) of a single positron to these systems increases by an increment of 0.2-0.3 eV as the atomic number of the alkali atom is increased. It is found that the positron prefers a location in the more electronegative regions of such molecules, similarly as has been found in earlier calculations for the urea and acetone molecules. The positron orbital itself possesses a diffuse charge distribution with relatively small expectation values of the kinetic energy in all four systems considered. Each of the four positronic molecules is stable with respect to formation of either positronium (Ps) or HPs according to the present calculations. Relatively large changes in the equilibrium bond distance of the hydrides occur as a result of the positron interaction. The importance of bond dipole moments in producing the binding of positrons to molecules is discussed, as well as the role that the electronegativity of the constituent atoms plays in determining the magnitude of the PA for a given system.     

Zur Thermodynamik der Mischungen von 1,2-Dibromäthan mit Benzol und Cyclohexan: Aktivitätskoeffizienten und Freie Mischungsenthalpie aus Bestimmungen der Schmelzkurve

Zusammenfassung Neckel undVolk ¹ haben Dampfdruckmessungen am System 1,2-Dibromäthan—Benzol ausgeführt und in einer weiteren Arbeit² mit Hilfe von Messungen der Dielektrizitätskonstante Angaben über das Konformationsgleichgewicht von Dibromäthan und Dichloräthan in Mischungen mit Benzol und Cyclohexan gemacht. Gleichzeitig haben sie die Freie Mischungsenthalpie aller vier Systeme berechnet. In dieser Arbeit wird nun die Freie Mischungsenthalpie der Systeme Dibromäthan—Benzol und Dibromäthan—Cyclohexan auf Grund von Messungen der Schmelzkurve ermittelt. Danach zeigt das System Dibromäthan—Benzol etwas schwächer positive Abweichungen vom idealen Mischungsverhalten, alsNeckel undVolk ¹ aus ihren Dampfdruck-messungen ableiten. Hingegen zeigt das System Dibromäthan—Cyclohexan sehr stark positive Abweichungen vom idealen Mischungsverhalten, im Gegensatz zu den Voraussagen vonNeckel undVolk ². Doch kann der größte Teil der Differenz zwischen Voraussage und experimentellem Verhalten beseitigt werden, wenn man die Dihalogenäthanmischungen als pseudoternäre Systeme behandelt. Die Angaben vonNeckel undVolk ² über die Variation des Konformationsgleichgewichts von Dibromäthan in den Mischungen mit Benzol und Cyclohexan und über die spezielle Wechselwirkung zwischen der polarengauche-Form von Dibromäthan und Benzol können im wesentlichen bestätigt werden.

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Neckel andVolk have measured vapour pressures in the system 1,2-dibromoethane-benzene; in a second paper, they used dielectric measurements to infer the conformation equilibrium of dibromoethane and dichloroethane in mixtures with benzene and cyclohexane. Furthermore, they have calculated the free enthalpy of mixing of all four systems. In this paper, the melting curves of the dibromoethane-benzene and the dibromoethane-cyclohexane systems are determined and the free enthalpy of mixing is deduced. According to our measurements, the dibromoethane-benzene system deviates somewhat less from ideal behaviour thanNeckel andVolk conclude from their vapour pressure measurements. On the other hand, the dibromoethane-cyclohexane system shows contrary to the predictions ofNeckel andVolk strong positive deviations from ideal behaviour. Most of these discrepancies can be overcome by treating mixtures with dihalogenethanes consistently as pseudoternary mixtures. The statements ofNeckel andVolk concerning the variation of the conformation equilibrium in mixtures with benzene and cyclohexane and about the specific interaction between the polar gauche-dibromoethane and benzene are confirmed.

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Mit 9 Abbildungen

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Herrn Professor Dr.Leopold Schmid zu seinem 70. Geburtstag in Verehrung gewidmet.