Berichte der Bunsengesellschaft für physikalische Chemie最新文献

First principles periodic Hartree-Fock calculations of Li:MnO, Li_xMnO₂ and CaMnO₃ are reported from which direct evidence is presented to indicate that the valence state of Mn remains essentially d⁵ throughout the series. The net spin moment on Mn, on the other hand, follows that convential change from ∼5μ_B to ∼3μ_B associated with the valence states Mn(II), Mn(III), Mn(IV).

The reaction of Si atoms with SiCl₄ was studied behind reflected shock waves at temperatures between 1530 and 1800 K and pressures around 1.7 bar by applying atomic resonance absorption spectroscopy (ARAS) for time-resolved measurement of Si atoms. The thermal decomposition of a few ppm Si₂H₆ was used as source for Si-atoms. The presence of an excess of SiCl₄ causes a fast consumption of Si atoms, which follows a pseudo-first-order rate law. The rate coefficient for the reaction of Si atoms with SiCl₄

was determined to be:

k₁ = 4.0±0.2×10¹³cm³ mol⁻¹s⁻¹

with no observable temperature dependence in the temperature range of the present study.

The infrared spectrum of fulminic acid, H¹³CNO, has been analyzed in the range 700–3600 cm⁻¹. More than 90 new vibrational levels have been identified. Power series coefficients of these levels are given.

Every vibrational level and its rotational levels are locally or globally perturbed. It was possible to classify most of the interactions into a grand network of Coriolis- and/or Fermi-type resonance systems, similar to that described for the parent species H¹²CNO, by using the previously known basic resonance systems 00010/00002 and 00100/00004. In addition, as for H¹²CNO, another basic resonance for H¹³CNO was identified as 01000/00111, leading to the system 00015/01000/00103/(00111), corresponding to a resonance involving the same states in the parent species. As a consequence of the interactions, many so-called “resonance-enhanced” rovibrational subbands have been assigned. The identification and partial analysis of the resonance systems have been carried out, first with the help of different representations of reduced term values and second, by determining the J-value separation between e and f crossing points. The five main resonance systems will be discussed in this paper.

The reactions of CF₃O radicals with (1) NO and (2) NO₂ were studied using two different experimental techniques. A laser photolysis/LIF detection method was applied for measuring the rate constants as a function of temperature (T = 222–302 K) and total pressure (p_tot = 7–107 mbar). Whereas the reaction with (1) NO was found to be independent of temperature and pressure with k₁ = (4.5±1.2)×10⁻¹¹ cm³ s⁻¹, the reaction with (2) NO₂ was found to be dependent on both of these variables. The temperature dependence of k₂ in the high pressure limit can be given by the expression k_2,∝ (T) = (8±5)×10⁻¹³ exp ((863±194) K/T) cm³ s⁻¹. The product distributions of the two reactions were determined in separate experiments using steady-state photolysis combined with FTIR spectroscopy. For reaction (1) only CF₂O was found as a reaction product with a yield of 0.93±0.10, independent of temperature. For reaction (2) several products (CF₃ONO₂, CF₂O, FNO₂) were identified, the overall yield, however, is dominated (≥90%) by the recombination product CF₃ONO₂. A theoretical analysis of the detailed mechanisms of both reactions was made by performing ab initio energy and geometry predictions in combination with RRKM calculations. Both reactions were found to proceed via an initial addition mechanism involving the CF₃ONO_x (x = 1, 2) intermediate and a four-center transition state. A direct abstraction of an F atom by NO or NO₂ can be excluded.

The kinetics of the bimolecular reactions OH+C₂H₂+M ⟺ C₂H₂OH+M (1) and OH+C₂H₄+M ⟺ C₂H₄OH+M (2) have been investigated over an extended pressure (1–130 bar) and temperature (300–800 K) range. The OH radicals have been generated by laser flash photolysis of suited precursors and their decays have been measured by saturated laser-induced fluorescence (SLIF) under pseudo-first-order conditions. The pressure dependences have been analyzed by constructing falloff curves at fixed temperatures leading to reliable extrapolations towards the high pressure limiting rate constants k_∞. In the given temperature range these rate constants are represented as k_1,∞ = 3.8×10⁻¹¹ exp (–910 K/T) cm³ molecule⁻¹ s⁻¹ and as k_2,∞ = 1.0×10⁻¹¹ cm³ molecule⁻¹ s⁻¹. At temperatures above 700 K biexponential decay curves have been obtained. The chemical equilibria of reactions (1) and (2) could be determined. By a third law analysis the equilibrium constants have been evaluated with reaction enthalpies for the addition complex C₂H₂OH of δ_IH^o₁ (O K) = -(146 ± 10) kJ/mol and for C₂H₄OH of δ_IH^o₂ (O K) = -(123 ± 6) kJ/mol, respectively. The two equilibrium constants are given by K_1,eq = (5.4±2.2)×10⁻² (T/K)^−1.7±0.2 exp ((17560±1200) K/T) bar⁻¹ and K_2,eq = 2.1 × 10⁻² (T/K)^−95±0.1 × exp ((14780±720) K/T) bar⁻¹, respectively.

In this publication we have studied molecular details of the solvent layer and the counterion distribution around sodium octanoate micelles. The results were obtained from computer experiments using molecular dynamics simulations. From the model it was possible to calculate the radial distribution functions, which give informations on the average distance between water molecules and the polar surfactant head groups. We observed different types of solvent layers. From these experiments it was also possible to calculate the number of hydrogen bonds between surrounding water molecules and the polar surfactant head groups. These results coincide well with experimental data and with other types of computer experiments. In analogy to water molecules it was also possible to get informations on the distribution of sodium counterions around the charged micelle. These results are in general agreement with experimental and theoretical data and they can be used to calculate Coulomb interactions and the net surface charge of the micellar aggregates.

Far infrared laser magnetic resonance (FIR-LMR) spectra of CF₃, CHF₂, and CH₂F radicals were observed in the 300–800 μm wavelength region in the reactions of F atoms with a series of different hydrocarbon and partially fluorinated hydrocarbon molecules. To identify the carriers of the observed resonance patterns and to exclude or identify contamination of the spectra by additional resonances from other paramagnetic species, numerous chemical tests were developed and performed. With optimized sources and the chemical tests in hand, many spectra could be unambiguously attributed to CF₃, CHF₂, and CH₂F, respectively. The present study reports the first gas phase detection of CHF₂ radicals in their ground electronic state.