On the studies of the vibrational spectra of cluster [Mo2O2S2(S2)2]2-

IR and Raman spectra of [Mo₂O₂S₂(S₂)₂]^2- were reported. The resonance Raman spectra and the depolarization ratios in CH₃CN solution were measured. By using the data of crystal structure, the simplified normal coordinate calculation of the stretching vibrations for anion [Mo₂O₂S₂(S₂)₂]^2- was performed. The results obtained are useful to assign the vibrational bands of some Mo-Fe-S clusters.     

[Mo2O2S2(S2)2][2-]的振动光谱研究

本文测定了原子簇化合物[Mo2O2S2(S2)2][2-]的红外和拉曼光谱,并在乙腈溶液中测得其共振拉曼光谱和退偏振比。利用X光晶体结构数据,对此阴离子的伸缩振动作了简化的正则坐标分析计算。所得结果可以帮助分析和归属一些Mo-Fe-S原子簇化合物的振动光谱。     

Kinetics of the reactions of the CHBr2 and CHBr2O2 radicals with O2 and NO

When bromoform (CHBr3) is photolyzed at 266 or 303 nm in the presence of O2 and NO, the formation of secondary Br atoms is observed. By following the rate of growth of this secondary Br atom signal as a function of conditions, rate constants have been determined for the reactions CHBr2 + O2, CHBr2 + NO (both pressure-dependent), and CHBr2O2 + NO (k(2a) = (1.74 +/- 0.16) x 10(-11) cm3 molecule(-1) s(-1) at 23 degrees C). By measuring the amplitude of the secondary Br signal compared to the primary Br formed in the initial photolysis, it is established that the CHBr2O radical spontaneously decomposes to form CHBrO + Br at least 90%, and probably 100%, of the time, in agreement with previous work and with recent ab initio calculations. A survey of four other polybrominated methanes, CH2Br2, CHClBr2, CF2Br2, and CBr4, shows that they all generate secondary Br atoms when photolyzed at 266 nm in the presence of O2 and NO, suggesting that their reaction sequences are similar to that of bromoform.     

A study of the unimolecular dissociation of the 2-buten-2-yl radical via the 193 nm photodissociation of 2-chloro-2-butene

This work investigates the unimolecular dissociation of the 2-buten-2-yl radical. This radical has three potentially competing reaction pathways: C-C fission to form CH3 + propyne, C-H fission to form H + 1,2-butadiene, and C-H fission to produce H + 2-butyne. The experiments were designed to probe the branching to the three unimolecular dissociation pathways of the radical and to test theoretical predictions of the relevant dissociation barriers. Our crossed laser-molecular beam studies show that 193 nm photolysis of 2-chloro-2-butene produces 2-buten-2-yl in the initial photolytic step. A minor C-Cl bond fission channel forms electronically excited 2-buten-2-yl radicals and the dominant C-Cl bond fission channel produces ground-state 2-buten-2-yl radicals with a range of internal energies that spans the barriers to dissociation of the radical. Detection of the stable 2-buten-2-yl radicals allows a determination of the translational, and therefore internal, energy that marks the onset of dissociation of the radical. The experimental determination of the lowest-energy dissociation barrier gave 31 +/- 2 kcal/mol, in agreement with the 32.8 +/- 2 kcal/mol barrier to C-C fission at the G3//B3LYP level of theory. Our experiments detected products of all three dissociation channels of unstable 2-buten-2-yl as well as a competing HCl elimination channel in the photolysis of 2-chloro-2-butene. The results allow us to benchmark electronic structure calculations on the unimolecular dissociation reactions of the 2-buten-2-yl radical as well as the CH3 + propyne and H + 1,2-butadiene bimolecular reactions. They also allow us to critique prior experimental work on the H + 1,2-butadiene reaction.     

DSC study of the kinetics of the thermal dehydration of BaCl2 · 2H2O and BaCl2 · H2O

The kinetics of the thermal dehydration of various kinds of BaCl₂ · 2H₂O and of BaCl₂ · H₂O are investigated using a differential scanning calorimeter. The loss of H₂O proceeds in two steps: BaCl₂ · 2H₂O→BaCl₂ · H₂O→BaCl₂ and is therefore revealed by two endothermic peaks. In the experiments at varying temperature both steps follow a contracting-circle law, after an initial acceleratory stage according to a (n=2) power law. In the experiments at constant temperature, after an initial acceleratory stage according to a (n=2) power law, both steps (except BaCl₂ · 2H₂O single-crystals which follow a contracting-circle law) follow an Avrami-Erofeev law (withn=2) in the form used by Galwey and Jacobs. The activation energies for the various steps are compared and the different kinetic behaviour is discussed.     

Electronic structure and one-electron properties of the MoO2Cl2 molecule. Electronic spectra of the MoO2Cl2, MoO2Br2 and WO2Br2 molecules

The SCF-X -SW method in an overlapping atomic spheres approximation has been used to calculate the electronic structure, ionization potentials, energies and oscillator strengths of the allowed optical transitions and also some of the one-electron properties of the MoO₂Cl₂ molecule. The electronic absorption spectra of vapours over molybdenum and tungsten dioxodibromides have been measured. Interpretation of the experimental electronic absorption spectra of the MoO₂Cl₂, MoO₂Br₂ and WO₂Br₂ molecules is discussed.     

Syntheses on the basis of 2H-chromen-2-one and 2H-chromene-2-thione

4-Hydroxy-2H-chromen-2-one and 4-hydroxy-2H-chromene-2-thione reacted with allyl bromide, 1,1,3-trichloroprop-1-ene, and 1,3-dichlorobut-2-ene to give the corresponding ethers, which were oxidized to (2-oxo-2H-chromen-4-yloxy)acetic acid with potassium permanganate, and various derivatives of that acid were obtained. 3-(3,3-Dichloroprop-2-enyl)-7-hydroxy-4-methyl-2H-chromen-2-one and 3-(3,3-dichloroprop-2-enyl)-7-hydroxy-4-methyl-2H-chromene-2-thione were synthesized, and some their transformations were studied.     

An ab initio study of the relative stabilities of the isomers of CH2N2 and SiH2N2

Ab initio SCF calculations of the equilibrium geometries have been carried out on nine possible isomers of MH₂N₂, where M = C or Si, and compared with the results of MNDO calculations. The results for the carbon compounds are in good agreement with available experimental data, but in the case of the silicon compounds, the molecules are predicted to be unstable with respect to decomposition to SiH₂ and N₂. The inclusion of electron correlation at the MP3 level does not alter the order of the relative stabilities, although the importance of the correlation contribution varies substantially between the different isomers.     

On the shift of H2O between the carbons of the radical cation [CH2CH2OH2]+˙

Computations predict that H₂O will shift rapidly between the carbons of \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop {\rm C}\limits^{\rm .} {\rm H}_2 {\rm CH}_2 \mathop {\rm O}\limits^ + {\rm H}_2 $\end{document} over most of the energy range between the threshold for formation of the ion and the onset of its decomposition. This prediction is important to understanding the relationships and contrasts between the chemistries of free radicals and carbonium ions. We present experimental evidence that the theoretical predictions are correct.     

A systematic computational study of the reactions of HO2 with RO2: the HO2 + CH2ClO2, CHCl2O2, and CCl3O2 reactions

Potential energy surfaces for the reactions of HO(2) with CH(2)ClO(2), CHCl(2)O(2), and CCl(3)O(2) have been calculated using coupled cluster theory and density functional theory (B3LYP). It is revealed that all the reactions take place on both singlet and triplet surfaces. Potential wells exist in the entrance channels for both surfaces. The reaction mechanism on the triplet surface is simple, including hydrogen abstraction and S(N)2-type displacement. The reaction mechanism on the singlet surface is more complicated. Interestingly, the corresponding transition states prefer to be 4-, 5-, or 7-member-ring structures. For the HO(2) + CH(2)ClO(2) reaction, there are two major product channels, viz., the formation of CH(2)ClOOH + O(2) via hydrogen abstraction on the triplet surface and the formation of CHClO + OH + HO(2) via a 5-member-ring transition state. Meanwhile, two O(3)-forming channels, namely, CH(2)O + HCl + O(3) and CH(2)ClOH + O(3) might be competitive at elevated temperatures. The HO(2) + CHCl(2)O(2) reaction has a mechanism similar to that of the HO(2) + CH(2)ClO(2) reaction. For the HO(2) + CCl(3)O(2) reaction, the formation of CCl(3)O(2)H + O(2) is the dominant channel. The Cl-substitution effect on the geometries, barriers, and heats of reaction is discussed. In addition, the unimolecular decomposition of the excited ROOH (e.g., CH(2)ClOOH, CHCl(2)OOH, and CCl(3)OOH) molecules has been investigated. The implication of the present mechanisms in atmospheric chemistry is discussed in comparison with the experimental measurements.     

Synthesis of Gels in the System Na2O-ZrO2-SiO2

Gels have been synthesized in the SiO₂-Na₂O-ZrO₂ system and calcined at various temperatures up to 700°C. They have been studied by infrared absorption spectroscopy. The position of the asymmetric stretching frequency of the SiO₄ unit is used as a tracer of the homogeneity. It is shown that sodium increases the solubility of zirconium in the silica matrix as already observed in fused glasses.     

A systematic computational study of the reactions of HO2 with RO2: the HO2 + C2H5O2 reaction

The reaction of HO2 with C2H5O2 has been studied using the density functional theory (B3LYP) and the coupled-cluster theory [CCSD(T)]. The reaction proceeds on the triplet potential energy surface via hydrogen abstraction to form ethyl hydroperoxide and oxygen. On the singlet potential energy surface, the addition-elimination mechanism is revealed. Variational transition state theory is used to calculate the temperature-dependent rate constants in the range 200-1000 K. At low temperatures (e.g., below 300 K), the reaction takes place predominantly on the triplet surface. The calculated low-temperature rate constants are in good agreement with the experimental data. As the temperature increases, the singlet reaction mechanism plays more and more important role, with the formation of OH radical predominantly. The isotope effect of the reaction (DO2 + C2D5O2 vs HO2 + C2H5O2) is negligible. In addition, the triplet abstraction energetic routes for the reactions of HO2 with 11 alkylperoxy radicals (CnHmO2) are studied. It is shown that the room-temperature rate constants have good linear correlation with the activation energies for the hydrogen abstraction.     

Investigation on the mechanism and applications of the reaction Cl_2+2HBr=2HCl+Br_2

The mechanism of reaction CI2+2HBr=2HCI+Br2 has been carefully investigated with density functional theory (DFT) at B3LYP/6-311G** level. A series of three-centred and four-centred transition states have been obtained. The activation energy (138.96 and 147.24 kJ/mol, respectively) of two bimolecular elementary reactions CI2+HBr→HCI+BrCI and BrCI+HBr→HCI+Br2 is smaller than the dissociation energy of CI2, HBr and BrCI, indicating that it is favorable for the title reaction occurring in the bimolecular form. The reaction has been applied to the chemical engineering process of recycling Br2 from HBr. Gaseous CI2 directly reacts with HBr gas, which produces gaseous mixtures containing Br2, and liquid Br2 and HCI are obtained by cooling the mixtures and further separated by absorption with CCI4. The recovery percentage of Br2 is more than 96%, and the CI2 remaining in liquid Br2 is less than 3.0%. The paper provides a good example of solving the difficult problem in chemical engineering with basic theory.     

CRTA Study of the Reduction of UO2F2 into UO2 by Dry H2

The reduction of UO₂F₂ by dry H₂ was studied by Controlled Rate EGA, with a special set-up operating under a gas flow under atmospheric pressure. At the constant transformation rate selected, this reduction apparently takes place in one main step, around 450°C (for a total duration of 100 h), followed by a small exothermic step. The final product is a stoichiometric, well crystallized UO₂. XRD analysis shows the occurrence of two successive intermediates of which one has a structure close to that of UO₂, but with interstitial fluorine atoms. This revised version was published online in August 2006 with corrections to the Cover Date.     

Ab initio investigation of the potential energy surfaces of C2H2F2 and C2H2F2+

Ab initio MO calculations have been performed for neutral and cationic C₂H₂F₂ structures. Olefinic and carbene structures are investigated for the neutral isomers, while olefinic, carbene, and fluoronium-type cations are found. Stability orders and rotational barriers are discussed in terms of orbital and Coulomb interaction. Contrary to previous studies, the higher stability of the geminal isomers is interpreted to be caused by Coulomb attraction.