Thermal and kinetic analysis of uranium salts

The thermal decomposition kinetics of UO₂C₂O₄·3H₂O were studied by TG method in a flowing nitrogen, air, and oxygen atmospheres. It is found that UO₂C₂O₄·3H₂O decomposes to uranium oxides in four stages in all atmosphere. The first two stages are the same in the whole atmosphere that correspond to dehydration reactions. The last two stages correspond to decomposition reactions. Final decomposition products are determined with X-Ray powder diffraction method. Decomposition mechanisms are different in nitrogen atmosphere from air and oxygen atmosphere. The activation energies of all reactions were calculated by model-free (KAS and FWO) methods. For investigation of reaction models, 13 kinetic model equations were tested and correct models, giving the highest linear regression, lowest standard deviation, and agreement of activation energy value to those obtained from KAS and FWO equations were found. The optimized value of activation energy and Arrhenius factor were calculated with the best model equation. Using these values, thermodynamic functions (??H ^*, ??S ^*, and ??G ^*) were calculated.     

CoC2O4·2H2O在空气中的热分解动力学研究

纳米Co3O4具有尖晶石结构,Co3 占据八面体位,具有较高的晶体场稳定化能,在空气中低于800℃时十分稳定,是优良的催化材料[1]。Co3O4还可以作为高比能锂离子电池负极材料具有非常好的电化学活性,充放电容量高达960m A h·g-1。纳米Co3O4在紫外、可见及近红外区域都有良好的吸收效果,因此,在隐身技术、保温节能技术等领域具有潜在的应用前景。所以,Co3O4超细粉体的制备和应用研究具有十分重要的意义。我们合成了草酸盐先驱物制备纳米Co3O4用作隐身材料,因此对先驱物的热分解过程研究是十分必要的。热分析方法在了解先驱物热分解反应的物理…     

Fragmentation of 1- and 3-methoxypropene ions another part of the C4H8O+• potential energy surface

The fragmentation mechanisms of metastable ionized 1? and 3?methoxypropene have been examined in detail by using ionization and appearance energy measurements, metastable ion and collisional activation mass spectra, and a variety of isotopically labeled molecules. These metastable C₄H₈O^+? ions fragment by loss of H; CH₃, and H₂CO, and the experimental observations allowed the construction of the potential energy diagram which describes their interconversion and the participation of four other distonic and carbene C₄H₈O^+? ions. It was found that these two methyl alkenyl ether ions had no common reaction channel with either the 2?methoxy isomer or with any of the alcohol, keto, or enol C₄H₈O^n+? isomers which previously have been extensively studied.     

Interaction of zinc oxide clusters with molecules related to the sulfur vulcanization of polyolefins ("rubber")

The vulcanization of rubber by sulfur is a large‐scale industrial process that is only poorly understood, especially the role of zinc oxide, which is added as an activator. We used the highly symmetrical cluster Zn₄O₄ (T_d) as a model species to study the thermodynamics of the initial interaction of various vulcanization‐related molecules with ZnO by DFT methods, mostly at the B3LYP/6‐31+G* level. The interaction energy of Lewis bases with Zn₄O₄ increases in the following order: CO62H₄3H₆2S₂<1,4‐C₅H₈2O2S3N?CH₃COO^?. The corresponding binding energies range from ?57 to ?262 kJ mol^?1. However, Brønsted acids react with the Zn₄O₄ cluster with proton transfer from the ligand molecule to one of the oxygen atoms of Zn₄O₄, and these reactions are all strongly exothermic [binding energies [kJ mol^?1] in parentheses: H₂O (?183), MeOH (?171), H₂S (?245), MeSH (?230), C₃H₆ (?121), and CH₃COOH (?255)]. The important vulcanization accelerator mercaptobenzothiazole (C₇H₅NS₂, MBT) containing several donor sites reacts with the Zn₄O₄ cluster with proton transfer from the NH group to one of the oxygen atoms of ZnO, and in addition the exocyclic thiono sulfur atom and the nitrogen atom coordinate to one and the same zinc atom, resulting in a binding energy of ?247 kJ mol^?1. A second isomer of [(MBT)Zn₄O₄] with a strong O? H???N hydrogen bond rather than a Zn? N bond is only slightly less stable (binding energy ?243 kJ mol^?1). The NH form of free MBT is 36 kJ mol^?1 more stable than the tautomeric SH form, while the sulfurized MBT derivative benzothiazolyl hydrodisulfide C₇H₅NS₃ (BtSSH) is most stable with the connectivity >CSSH.     

Thermal Decomposition and Dehydration Kinetics of Tetra(piperidinium) Octamolybdate Tetrahydrate in Air

Thermal decomposition of tetra(piperidinium) octamolybdate tetrahydrate, [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O, was investigated in air by means of TG‐DTG/DTA, DSC, TG‐IR and SEM. TG‐DTG/DTA curves showed that the decomposition proceeded through three well‐defined steps with DTA peaks closely corresponding to mass loss obtained. Kinetics analysis of its dehydration step was performed under non‐isothermal conditions. The dehydration activation energy was calculated through Friedman and Flynn‐Wall‐Ozawa (FWO) methods, and the best‐fit dehydration kinetic model function was estimated through the multiple linear regression method. The activation energy for the dehydration step of [C₅H₁₀NH₂]₄[Mo₈O₂₆]·4H₂O was 139.7 kJ/mol. The solid particles became smaller accompanied by the thermal decomposition of the title compound.     

Photoionization and Dissociation Study of 2-Methyl-2-propen-1-ol: Experimental and Theoretical Insights

The photoionization and dissociation of 2-methyl-2-propen-1-ol (MPO) have been investigated by using molecular beam experimental apparatus with tunable vacuum ultravioletsynchrotron radiation in the photon energy region of 8.0-15.5 eV. The photoionization efficiency (PIE) curves for molecule ion and fragment ions: C₄H₈O⁺、C₄H₇O⁺、C₃H₅O⁺、C₄H₇⁺、C₄H₆⁺、C₄H₅⁺、C₂H₄O⁺、C₂H₃O⁺、C₃H₆⁺、C₃H₅⁺、C₃H₃⁺、CH₃O⁺、CHO⁺ have been measured, and the ionization energy (IE) and the appearance energies (AEs) of the fragment ions have been obtained. The stable species and the first order saddle points have been calculated on the CCSD(T)/cc-pvTZ//B3LYP/6-31+G(d,p) level. With combination of theoretical and experimental results, the dissociative photoionization pathways of 2-methyl-2-propen-1-ol are proposed. Hydrogen migrations within the molecule are the dominant processes in most of the fragmentation pathways of MPO.     

Photofragmentation of 2‐Deoxy‐D‐Ribose Molecules in the Gas Phase

We have measured the synchrotron‐induced photofragmentation of isolated 2‐deoxy‐D ‐ribose molecules (C₅H₁₀O₄) at four photon energies, namely, 23.0, 15.7, 14.6, and 13.8 eV. At all photon energies above the molecule′s ionization threshold we observe the formation of a large variety of molecular cation fragments, including CH₃⁺, OH⁺, H₃O⁺, C₂H₃⁺, C₂H₄⁺, CH_xO⁺ (x=1,2,3), C₂H_xO⁺ (x=1–5), C₃H_xO⁺ (x=3–5), C₂H₄O₂⁺, C₃H_xO₂⁺ (x=1,2,4–6), C₄H₅O₂⁺, C₄H_xO₃⁺ (x=6,7), C₅H₇O₃⁺, and C₅H₈O₃⁺. The formation of these fragments shows a strong propensity of the DNA sugar to dissociate upon absorption of vacuum ultraviolet photons. The yields of particular fragments at various excitation photon energies in the range between 10 and 28 eV are also measured and their appearance thresholds determined. At all photon energies, the most intense relative yield is recorded for the m/q=57 fragment (C₃H₅O⁺), whereas a general intensity decrease is observed for all other fragments— relative to the m/q=57 fragment—with decreasing excitation energy. Thus, bond cleavage depends on the photon energy deposited in the molecule. All fragments up to m/q=75 are observed at all photon energies above their respective threshold values. Most notably, several fragmentation products, for example, CH₃⁺, H₃O⁺, C₂H₄⁺, CH₃O⁺, and C₂H₅O⁺, involve significant bond rearrangements and nuclear motion during the dissociation time. Multibond fragmentation of the sugar moiety in the sugar–phosphate backbone of DNA results in complex strand lesions and, most likely, in subsequent reactions of the neutral or charged fragments with the surrounding DNA molecules.     

Thermal dehydration and decomposition of M[M(C2O4)2]·xH2O (x=3 forM=Sr(II) andx=6 forM=Hg(II))

Strontium(II) bis (oxalato) strontium(II) trihydrate, Sr[Sr(C₂O₄)₂]·3H₂O and mercury(II) bis (oxalato) mercurate(II) hexahydrate, Hg[Hg(C₂O₄)₂]·6H₂O have been synthesized and characterized by elemental analysis, reflectance and IR spectral studies. Thermal decomposition studies (TG, DTG and DTA) in air showed SrCO₃ was formed at ca. 500°C through the formation of transient intermediate of a mixture of SrCO₃ and SrC₂O₄ around 455°C. Sharp phase transition from γ-SrCO₃ to β-SrCO₃ indicated by a distinct endothermic peak at 900°C in DTA. Mercury(II) bis (oxalato) mercurate(II) hexahydrate showed an inclined slope followed by surprisingly steep slope in TG at 178°C and finally 98.66% of weight loss at 300°C. The activation energies (E ^*) of the dehydration and decomposition steps have been calculated by Freeman and Carroll and Flynn and Wall's method and compared with the values found by DSC in nitrogen. A tentative reaction mechanism for the thermal decomposition of Sr[Sr(C₂O₄)₂]·3H₂O has been proposed.     

Kinetic study of thermal degradation of di-, chlorodi- and triorganotin(IV) complexes of 2-[(2,6-dichlorodiphenyl)amino]benzene acetate

The organotin complexes of the general formulae R₂SnL₂, R₂SnLCl and R₃SnL where R = C₄H₉, C₆H₅, and C₇H₇ and L = 2-[(2,6-dichlorodiphenyl)amino]benzene acetate, were subjected to thermal decomposition by thermogravimetric analysis (TGA). The decomposition of these compounds occurs mostly in two steps. Kinetic parameters such as order of reaction (n), activation energy (Ea), enthalpy (ΔH^?) and entropy (ΔS^?) of activation were calculated by using the Coats and Horowitz methods. The calculated values are in good agreement with observed TG values that confirm the structural integrity of the complexes.     

Kinetic energy release distribution in the fragmentation of energy-selected iodopropane ions

The technique of threshold photoelectron-photoion coincidence (PEPICO) has been employed to determine the average kinetic energy release and the kinetic energy release distribution (KERD) for the iodine loss from 1- and 2-iodopropane ions as a function of the ion internal energy. The KERDs at all precursor-ion energies investigated (0–3 eV excess energy) have the shape of statistically expected distributions, 1-iodopropane ions which dissociate with an apparent 0.16 eV reverse activation barrier, are shown to isomerize at low energies prior to dissociation, to produce subsequently the 2-propyl C₃H₇^? structure. At high energies they may form a different C₃H₇^? isomer. The experimentally observed average kinetic energy releases are approximately a factor of 2 greater than expected statistically suggesting that not all vibrational modes participate in the energy disposal. The secondary dissociation of the C₃H₇^? isomers to C₃H₃ which is inhibited by a reverse activation barrier of = 0.4 eV indicates that the 1- and 2-iodopropane ions dissociate 75% and 60% respectively, to form the excited 1(²P_1/2) atoms.     

Dissociative photoionization of isoprene: experiments and calculations

Vacuum ultraviolet (VUV) dissociative photoionization of isoprene in the energy region 8.5–18 eV was investigated with photoionization mass spectroscopy (PIMS) using synchrotron radiation (SR). The ionization energy (IE) of isoprene as well as the appearance energies (AEs) of its fragment ions C₅H₇⁺, C₅H₅⁺, C₄H₅⁺, C₃H₆⁺, C₃H₅⁺, C₃H₄⁺, C₃H₃⁺ and C₂H₃⁺ were determined with photoionization efficiency (PIE) curves. The dissociation energies of some possible dissociation channels to produce those fragment ions were also determined experimentally. The total energies of C₅H₈ and its main fragments were calculated using the Gaussian 03 program and the Gaussian‐2 method. The IE of C₅H₈, the AEs for its fragment ions, and the dissociation energies to produce them were predicted using the high‐accuracy energy model. According to our results, the experimental dissociation energies were in reasonable agreement with the calculated values of the proposed photodissociation channels of C₅H₈. Copyright © 2009 John Wiley & Sons, Ltd.     

(Zn1-xMnx)C2O4·2H2O在空气中的热分解动力学研究

用热分析（TG-DTG/DTA）、X射线衍射（XRD）技术和透射电镜（TEM）研究了固态物质Zn_1-xMn_xC₂O₄•2H₂O在空气中热分解的过程。热分析结果表明，Zn_1-xMn_xC₂O₄•2H₂O在空气中分两步分解，其失重率与理论计算失重率相吻合。 XRD和TEM结果表明，Zn_1-xMn_xC₂O₄•2H₂O分解的最终产物为Zn_1-xMn_xO,其颗粒大小约为10-13 nm。在非等温条件下对Zn_1-xMn_xC₂O₄•2H₂O的热分解动力学进行了分析。用Friedman法和Flynn-Wall-Ozawa(FWO)法求取了分解过程的活化能E，并用多元线性回归给出了可能的机理函数。Zn_1-xMn_xC₂O₄•2H₂O两步热分解的活化能分别为155.7513 kJ/mol 和215.9397 kJ/mol。     

Dissociative Photoionization of 1,4-Dioxane with Tunable VUV Synchrotron Radiation

The photoionization and photodissociation of 1,4-dioxane have been investigated with a reflectron time-of-flight photoionization mass spectrometry and a tunable vacuum ultraviolet synchrotron radiation in the energy region of 8.0-15.5 eV. Parent ion and fragment ions at m/z 88, 87, 58, 57, 45, 44, 43, 41, 31, 30, 29, 28 and 15 are detected under supersonic conditions. The ionization energy of DX as well as the appearance energies of its fragment ions C₄H₇O₂⁺, C₃H₆O⁺, C₃H₅O⁺, C₂H₅O⁺, C₂H₄O⁺, C₂H₃O⁺, C₃H₅⁺, CH₃O⁺, C₂H₆⁺, C₂H₅⁺/CHO⁺, C₂H₄⁺ and CH₃⁺ was determined from their photoionization efficiency curves. The optimized structures for the neutrals, cations, transition states and intermediates related to photodissociation of DX are characterized at the B3LYP/6-31+G(d,p) level and their energies are obtained by G3B3 method. Possible dissociative channels of the DX are proposed based on comparison of experimental AE values and theoretical predicted ones. Intramolecular hydrogen migrations are found to be the dominant processes in most of the fragmentation pathways of 1,4-dioxane.     

Potential energy profiles for the unimolecular reactions of [C3H7S]+ Ions

Appearance energies were measured for several types of [C₃H₇S]⁺ ions. From these appearance energy values the heats of formation of the ions were calculated. For the isomeric ions that could not be generated in the mass spectrometer, the heats of formation were estimated by means of the isodesmic substitution method. Transition state energies for the decomposition to C₂H₄ and [CH₃S]⁺ along two pathways were determined from the appearance energies of these ions. Using the energy values, potential energy diagrams were constructed for the rearrangements and decompositions of the [C₃H₇S]⁺ ions. A supplementary ¹³C Clabelling experiment is described for the determination of the rearrangement pathway of [CH₃CH₂CH?SH]⁺ ions prior to decomposition.     

Stacking of Benzene with Metal Chelates: Calculated CCSD(T)/CBS Interaction Energies and Potential‐Energy Curves

Accurate values for the energies of stacking interactions of nickel‐ and copper‐based six‐membered chelate rings with benzene are calculated at the CCSD(T)/CBS level. The results show that calculations made at the ωB97xD/def2‐TZVP level are in excellent agreement with CCSD(T)/CBS values. The energies of [Cu(C₃H₃O₂)(HCO₂)] and [Ni(C₃H₃O₂)(HCO₂)] chelates stacking with benzene are ?6.39 and ?4.77 kcal mol^?1, respectively. Understanding these interactions might be important for materials with properties that are dependent on stacking interactions.     

Internal energy effects on metastable characteristics. The structure of [C3H7O]+ ions

The effect of changes in the internal energy distribution of the fragmenting ion on the ratio of metastable ion intensities for two competing fragmentation reactions has been investigated both theoretically and experimentally. Model calculations have shown that if the competing reactions have significantly different activation energies the metastable intensity ratio does depend on the internal energy distribution although large changes are necessary before the ratio changes by more than a factor of two. Experimentally the metastable characteristics of [C₃H₇O]⁺ ions of nominal structures [CH₃CH₂O⁺?CH₂] (I), [(CH₃)₂C?O⁺H] (II), [CH₃CH₂CH?O⁺H] (III) and [CH₃O⁺?CHCH₃] (IV) have been examined. For each structure the metastable characteristics are found to be distinctive and independent of changes in the internal energy distribution of the fragmenting ion where these changes result from altering the precursor of the [C₃H₇O]⁺ ions. It is suggested that these internal energy changes can be estimated from the fraction of [C₃H₇O]⁺ ions which fragment in the ion-source. It is concluded that structures I to IV represent stable and distinct ionic structures.     

稳定的气相二价阴离子C7H22-

采用HF, MP2, CCSD以及CISD方法,研究了二价阴离子C₇H₂^2-和C₇H₃^2-及其一价阴离子的几何结构振动频率。在理论上,我们得到了C₇H₂^2-和C₇H₃^2-能量最低结构分别为：C₂C(H₂)C₄^2-和C₂CHCHCHC₂^2-,而且均没有虚频。计算这两种结构所有可能的碎片化通道,碎片化能表明这两结构都不易解离为两个一价阴离子碎片。但是这两结构的垂直电离能和绝热电离能表明C₂C(H₂)C₄^2-是稳定的,但C₂CHCHCHC₂^2-是不稳定的。     

The nonisothermal decomposition kinetics of copper(II) complexes with phthalanilic acids and amino acids

Fifteen new kinds of mixed ligand complexes Cu(x‐P)A [P = 2‐(COO)C₆H₄CONH‐C₆H₄; x = H, 2‐Cl, 2‐CH₃, 2‐OCH₃, 4‐OCH₂CH₃; A = dehydronium Met, Leu, Phen] were synthesized. The thermal decomposition behavior of each complex is studied by TG. Coats‐‐Redfern, MacCallum‐‐Tammer, and Zsako methods are adopted to estimate the values of the apparent activation energy E_a, the activation entropy δS^≠, the reaction order n, and the frequency factor A. The results showed that the reaction order is 2/3 for each of the complex. Studies on the mechanism of the thermal decomposition reactions suggested that these reactions all fit the kinetic equation 1 ? (1 ? α)^1/3 = © 2003 Wiley Periodicals, Inc. Int J Chem Kinet 35: 623–628, 2003     

Some new cobalt(II) complexes: Synthesis,characterization and thermal studies

Cobalt(II) complexes of tetradentate Schiff bases of the type CoL [H₂L=C₂₀H₁₆N₂O₂ (H₂dsp), C₂₁H₁₈N₂O₂ (H₂dst), C₂₀H₁₅N₃O₄ (H₂ndsp) and C₁₆H₁₆N₂O₂ (H₂salen)] have been synthesized and characterized by UV-visible, IR, and magnetic studies. Various thermodynamic parameters have been calculated for the decomposition step using TG/DTA. C₂₀H₁₄N₂O₂Co complex has the minimum and C₁₆H₁₄N₂O₂Co complex has the maximum activation energy.This revised version was published online in November 2005 with corrections to the Cover Date.     

An unsymmetrical behavior of reactant units in the Kolbe�CSchmitt reaction

Paths of the Kolbe?CSchmitt reaction were investigated by the use of RB3LYP/6-311(+)G(d,p) density functional theory calculations. In a monomer model composed of C₆H₅O^?, Na⁺ and CO₂ affording sodium salicylate [C₆H₄(OH)CO₂ ^?Na⁺], a proton-shift step (Z Naturforsch 57a:812, 2002) was found to have an unrealistically large activation energy. In consideration of the phenol volatilization in the Kolbe??s experiment and the need of the linearity of the proton-transfer path, a dimer model was constructed. Again, a mutual proton-transfer step has a large activation energy. Alternatively, in a dimer model, a transfer path where the phenoxide ion in one monomer acts as a proton acceptor was found to have a reasonable energy. Addition of one more sodium ion leads to the significant lowering of activation energies. Thus, in the dimer, two monomers behave differently (A?+?A????A?+?B); one is as if it were a catalyst.