Heat For Reaction Research Articles

Direct dynamics study on the mechanism and the kinetics of the reaction of CH3NH2 with OH

AbstractA theoretical study of the mechanism and the kinetics for the hydrogen abstraction reaction of methylamine by OH radical has been presented at the CCSD(T)/6‐311 ++G(2d,2p)//CCSD/6‐31G(d) level of theory. Our theoretical calculations suggest a stepwise mechanism involving the formation of a prereactant complex in the entrance channel and a preproduct complex in the exit channel, for the two hydrogen abstraction channels involving the methyl and amine groups. For clarity, the diagram of potential for the reaction is given. The calculated standard reaction enthalpies are −98.48 and −76.50 kJ mol−1 and barrier heights are 0.36 and 25.25 kJ mol−1, respectively. The rate constants are evaluated by means of the improved canonical variational transition state theory with small‐curvature tunneling correction (ICVT/SCT) in the temperature range of 299–3000 K. The calculated results show that the rate constants at experimentally measured temperatures are in good agreement with the experimental values. It is shown that the calculated rate constants exhibit a non‐Arrhenius behavior. Moreover, the variational effect is obvious in the calculated temperature range. The dominant product channel is to form CH2NH2 and H2O via hydrogen abstraction from the CH3 group of CH3NH2 by OH in the calculated temperature range. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009

Thermodynamics of the hydrolysis reactions of α- d-galactose 1-phosphate, sn-glycerol 3-phosphate, 4-nitrophenyl phosphate, phosphocreatine, and 3-phospho- d-glycerate

Microcalorimetry, high-performance liquid chromatography (h.p.l.c.), and an enzymatic assay have been used to conduct a thermodynamic investigation of five phosphate hydrolysis reactions: {α- d-galactose 1-phosphate(aq) + H 2O(l) = d-galactose(aq) + orthophosphate(aq)} (1), { sn-glycerol 3-phosphate(aq) + H 2O(l) = glycerol(aq) + orthophosphate(aq)} (2), {4-nitrophenyl phosphate(aq) + H 2O(l) = 4-nitrophenol(aq) + orthophosphate(aq)} (3), {phosphocreatine(aq) + H 2O(l) = creatine(aq) + orthophosphate(aq)} (4), and {3-phospho- d-glycerate(aq) + H 2O(l) = d-glycerate(aq) + orthophosphate(aq)} (5). Calorimetrically determined enthalpies of reaction Δ r H(cal) were measured for reactions (1)–(5) and the apparent equilibrium constant K′ was measured for reaction (2). The p Ks and standard enthalpies of reaction Δ r H ∘ for the H + and Mg 2+ binding reactions of the reactants and products in the aforementioned reactions were obtained either from the literature or by estimation. A chemical equilibrium model was then used to calculate standard equilibrium constants K and standard enthalpies of reaction Δ r H ∘ for chemical reference reactions that correspond to the overall biochemical reactions that were studied experimentally. Property values from the literature and thermodynamic network calculations were used to obtain values of the equilibrium constants for the chemical reference reactions that correspond to the overall biochemical reactions (1). These values were compared with other results from the literature and also correlated with structural features. The results obtained in this study can be used in the chemical equilibrium model to calculate values of K′, the standard apparent Gibbs free energy changes Δ r G ′ ∘ , the standard apparent enthalpy changes Δ r H ′ ∘ , changes in binding of the proton Δ r N(H +), and the position of equilibrium for the overall biochemical reactions considered in this study over a reasonably wide range of temperature, pH, pMg [−log 10{ m(Mg 2+)/ m°}], and ionic strength I. Values of K′ and Δ r G′° under approximately physiological conditions ( T = 310.15 K, pH 7.0, pMg = 3.0, and I m = 0.25 mol · kg −1) have been calculated.

Thermodynamics of the hydrolysis reactions of 1,4-β- d-xylobiose, 1,4-β- d-xylotriose, d-cellobiose, and d-maltose

Microcalorimetry and high-performance liquid chromatography have been used to conduct a thermodynamic investigation of the following reactions: (1) 1 , 4 - β - d-xylobiose ( aq ) + H 2 O ( l ) = 2 d-xylose ( aq ) , (2) 1 , 4 - β - d-xylotriose + 2 H 2 O ( l ) = 3 d-xylose ( aq ) , (3) d-maltose ( aq ) + H 2 O ( l ) = 2 α - d-glucose ( aq ) , (4) d-cellobiose ( aq ) + H 2 O ( l ) = 2 α - d-glucose ( aq ) . The results of the equilibrium measurements were K = (1.46 ± 0.15) · 10 3 for reaction (1) and K = (551 ± 34) for reaction (3). Although it was not possible to measure directly a value for the equilibrium constant for reaction (4), it was possible to obtain the value K = 657 for this reaction via a thermochemical pathway calculation. The results of the calorimetric measurements were standard enthalpies of reaction Δ r H ∘ = (0.12 ± 0.26) kJ · mol −1 for reaction (1) and Δ r H ∘ = −(0.06 ± 0.18) kJ · mol −1 for reaction (2). It is noted that values of Δ r H ∘ for reactions (1) and (2) are equal to each other within their respective experimental errors. This fact is consistent with earlier observations that, for reactions involving the making/breaking of N saccharide linkages, the assignment of characteristic values of Δ r H ∘/ N or Δ r G ∘/ N or Δ r S ∘/ N for a specified linkage, is accurate in predicting the values of Δ r H ∘, Δ r G ∘, and Δ r S ∘ for reactions involving saccharides that contain multiples or combinations of such linkages. Also, the values of the standard entropy changes Δ r S ∘ for the hydrolysis reactions (3) and (4) fall into the range of values {(32 to 48) J · K −1 · mol −1)} previously noted for the hydrolysis of six-carbon disaccharides. In order to tie the results of this study into the thermochemical literature, a reaction catalog of related property values was created. Selected property values from this reaction catalog were then used to calculate “best” values of the standard Gibbs free energy of formation Δ f G ∘, the standard enthalpy of formation Δ f H ∘, the standard molar entropy S ∘ m, and the standard molar heat capacity C p ,m ∘ , for the substances of interest to this investigation.

Rhombohedral calcite precipitation from CO2-H2O-Ca(OH)2 slurry under supercritical and gas CO2 media

The formation of solid calcium carbonate (CaCO3) from aqueous solutions or slurries containing calcium and carbon dioxide (CO2) is a complex process of considerable importance in the ecological, geochemical and biological areas. Moreover, the demand for powdered CaCO3 has increased considerably recently in various fields of industry. The aim of this study was therefore to synthesize fine particles of calcite with controlled morphology by hydrothermal carbonation of calcium hydroxide at high CO2 pressure (initial PCO2=55 bar) and at moderate and high temperature (30 and 90°C). The morphology of precipitated particles was identified by transmission electron microscopy (TEM/EDS) and scanning electron microscopy (SEM/EDS). In addition, an X-ray diffraction analysis was performed to investigate the carbonation efficiency and purity of the solid product. Carbonation of dispersed calcium hydroxide ( ) in the presence of supercritical (PT=90 bar, T=90°C) or gaseous (PT=55 bar, T=30°C) CO2 led to the precipitation of sub-micrometric isolated particles (<1µm) and micrometric agglomerates (<5µm) of calcite. For this study, the carbonation efficiency (Ca(OH)2-CaCO3 conversion) was not significantly affected by PT conditions after 24 h of reaction. In contrast, the initial rate of calcium carbonate precipitation increased from 4.3 mol/h in the 90bar-90°C system to 15.9 mol/h in the 55bar-30°C system. The use of high CO2 pressure may therefore be desirable for increasing the production rate of CaCO3, carbonation efficiency and purity, to approximately 48 kg/m3h, 95% and 96.3%, respectively in this study. The dissipated heat for this exothermic reaction was estimated by calorimetry to be -32 kJ/mol in the 90bar-90°C system and -42 kJ/mol in the 55bar-30°C system.

Theoretical Study and Rate Constant Computation on the Reaction HFCO + OH → CFO + H2O

The potential energy surface, including the geometries and frequencies of the stationary points, of the reaction HFCO + OH is calculated using the MP2 method with 6-31+G(d,p) basis set, which shows that the direct hydrogen abstraction route is the most dominating channel with respect to addition and substitution channels. For the hydrogen abstraction reaction, the single-point energies are refined at the QCISD(T) method with 6-311++G(2df,2pd) basis set. The calculated standard reaction enthalpy and barrier height are -17.1 and 4.9 kcal mol(-1), respectively, at the QCISD(T)/6-311++G(2df,2pd)//MP2/6-31+G(d,p) level of theory. The reaction rate constants within 250-2500 K are calculated by the improved canonical variational transition state theory (ICVT) with small-curvature tunneling (SCT) correction at the QCISD(T)/6-311++G(2df,2pd)//MP2/6-31+G(d,p) level of theory. The fitted three-parameter formula is k = 2.875 x 10(-13) (T/1000)1.85 exp(-325.0/T) cm(3) molecule(-1) s(-1). The results indicate that the calculated ICVT/SCT rate constant is in agreement with the experimental data, and the tunneling effect in the lower temperature range plays an important role in computing the reaction rate constants.

Influence of Oxygen Addition on the Reaction of Propane Catalytic Dehydrogenation to Propylene over Modified Pt-Based Catalysts

The influences of oxygen addition to catalytic dehydrogenation system on the structure and the dehydrogenation performance of Pt-based catalysts were investigated. The results showed that a small amount of oxygen addition into the reaction system could greatly improve the catalytic performance of Pt−Sn/Ce-γ-Al2O3 catalyst although it evidently decreased the catalytic stability of Pt/γ-Al2O3, Pt−Sn/γ-Al2O3, and Pt/Ce-γ-Al2O3 catalysts. The addition of a small amount of oxygen can decrease the pressure of hydrogen, eliminate coke, and provide partial heat for catalytic dehydrogenation reaction. Hydrogen chemisorption results indicated that steam could reduce the interactions between metal and support, thus promoting the sintering of platinum particles. That adverse effect of steam on the structure on Pt−Sn/Ce-γ-Al2O3 was moderate, but it was serious on other Pt-based catalysts due to low-stability platinum particles. Both the promoting effect of Ce on the propane conversion and the inhibiting effect of Sn o...

A SOLUBILITY AND THERMODYNAMIC STUDY OF STRUVITE

Accumulation of magnesium ammonium phosphate hexahydrate (struvite) on surfaces in contact with wastewater, especially in anaerobic sludge digestion and post-digestion processes, is a widely reported problem in the wastewater treatment industry. The solubility and thermodynamic properties of struvite at different temperatures was studied. Struvite thermodynamic solubility products at temperatures between 10 and 60 °C were determined by variation of solution ionic strength and extrapolation to zero ionic strength, using an appropriate activity coefficient model. The pKsp value of struvite at 25°C was found to be 13.36(±0.07). The pKsp value for a temperature range of 10-60 °C varies from 14.36(±0.05) to 14.01(±0.03) with the minimum value of 13.17(±0.05) at 30°C. The effect of ionic strength, pH and temperature on struvite solubility was also studied. The solubility of struvite determined in deionized water was found to be 169.2 (±4.3) mg l-1 at 25°C, with the maximum value of 212.7 (±3.8) mg l-1 at 35°C. Standard enthalpy of reaction, ΔHγ °, calculated from the average Ksp values for the temperature range of 10-30 °C, was 23.62 Kcal mol-1. An analytical expression for the Ksp as a function of temperature has been developed by fitting experimental data.

Calcite precipitation from CO 2–H 2O–Ca(OH) 2 slurry under high pressure of CO 2

The formation of solid calcium carbonate (CaCO 3) from aqueous solutions or slurries containing calcium and carbon dioxide (CO 2) is a complex process of considerable importance in the ecological, geochemical and biological areas. Moreover, the demand for powdered CaCO 3 has recently increased considerably in various fields of industry. The aim of this study was therefore to synthesize fine particles of calcite with controlled morphology by hydrothermal carbonation of calcium hydroxide at high CO 2 pressure ( initial P CO 2 = 55 bar ) and at moderate and high temperatures (30 and 90 °C). The morphology of precipitated particles was identified by transmission electron microscopy (TEM/EDS) and scanning electron microscopy (SEM/EDS). In addition, an X-ray diffraction analysis was performed to investigate the carbonation efficiency and purity of the solid product. Carbonation of dispersed calcium hydroxide (Ca(OH) 2(s)+CO 2(aq)→CaCO 3(s)+H 2O) in the presence of supercritical ( P T=90 bar, T=90 °C) or gaseous ( P T=55 bar, T=30 °C) CO 2 led to the precipitation of sub-micrometric isolated particles (<1 μm) and micrometric agglomerates (<5 μm) of calcite. For this study, the carbonation efficiency (Ca(OH) 2–CaCO 3 conversion) was not significantly affected by pressure–temperature (PT) conditions after 24 h of reaction. In contrast, the initial rate of calcium carbonate precipitation increased from 4.3 mol/h in the “90 bar–90 °C” system to 15.9 mol/h in the “55 bar–30 °C” system. The use of high CO 2 pressure may therefore be desirable for increasing the production rate of CaCO 3, carbonation efficiency and purity, to approximately 48 kg/m 3 h, 95% and 96.3%, respectively, in this study. The dissipated heat for this exothermic reaction was estimated by calorimetry to be −32 kJ/mol in the “90 bar–90 °C” system and −42 kJ/mol in the “55 bar–30 °C” system.

Mathematical modelling of low-temperature hydrogen production with in situ CO 2 capture

Theoretical analysis of a process for low-temperature hydrogen production through steam methane reforming (SMR), based on the concept of adsorption-enhanced reaction, is presented. In the proposed process, mobile (pneumatically conveyed) adsorbent particles are passed through a stationary SMR catalyst monolith. Adsorbent regeneration is carried out in an external unit, thus decoupling the reaction and adsorbent regeneration steps, and allowing continuous operation. Heat for reaction is also supplied via the regeneration unit (via the thermal capacitance of the adsorbent), and thus effective energy integration is possible between the reactor and regenerator units. A mathematical model accounting for non-isothermal reaction and adsorption, mass transfer limited adsorption kinetics and non-linear (Langmuirian) adsorption equilibria, has been developed. The performance of the adsorptive reactor in terms of conversion enhancement is presented in this paper. Simulation results indicate considerable conversion enhancement through the use of a flowing adsorbent medium. The importance of the correct selection of operating parameters, i.e., adsorbent mass flow rate and temperature, on the process feasibility is also highlighted.

Standard molar enthalpies of formation of [RE(Gly)4(Im)(H2O)](ClO4)3 (RE=Eu, Sm)

The two complexes, [RE(Gly)4(Im)(H2O)](ClO4)3(s)(RE = Eu, Sm), have been synthesized and characterized. The standard molar enthalpies of reaction for the following reactions, RECl3·6H2O(s)+4Gly(s)+Im(s)+3NaClO4(s) = =[RE(Gly)4(Im)(H2O)](ClO4)3(s)+3NaCl(s)+5H2O(l), were determined by solution-reaction colorimetry. The standard molar enthalpies of formation of the two complexes at T = 298.15 K were derived as ΔfHmΘ {Eu(Gly)4(Im)(H2O)}(ClO4)3(s)} = = −(3396.6±2.3) kJ mol−1 and ΔfHmΘ {Sm(Gly)4(Im)(H2O)}(ClO4)3(s)} = −(3472.7±2.3) kJ mol−1, respectively.

Stochastic thermodynamics of chemical reaction networks

For chemical reaction networks in a dilute solution described by a master equation, the authors define energy and entropy on a stochastic trajectory and develop a consistent nonequilibrium thermodynamic description along a single stochastic trajectory of reaction events. A first-law like energy balance relates internal energy, applied (chemical) work, and dissipated heat for every single reaction. Entropy production along a single trajectory involves a sum over changes in the entropy of the network itself and the entropy of the medium. The latter is given by the exchanged heat identified through the first law. Total entropy production is constrained by an integral fluctuation theorem for networks arbitrarily driven by time-dependent rates and a detailed fluctuation theorem for networks in the steady state. Further exact relations such as a generalized Jarzynski relation and a generalized Clausius inequality are discussed. The authors illustrate these results for a three-species cyclic reaction network which exhibits nonequilibrium steady states as well as transitions between different steady states.

Growing Carbon Nanotube on Aluminum Oxides: An Inherently Safe Approach for Environmental Applications

Using micron-sized Al 2O 3 particles as carriers to grow carbon nanotubes (CNTs) under 700°C atmosphere of methane and hydrogen after pre-planted catalysts of Fe–Ni nanoparticles, those composite CNTs (CCNTs) have demonstrated several unique properties compared to CNTs—medium specific surface area and zeta potential, high adsorption capacity for metal ions, high recovery rate by acids, low decomposition heat for exothermal reaction, and so on. The adsorption behaviours of Pb 2+, Cu 2+ and Cd 2+ in aqueous solutions by CCNTs are in good agreement with the Langmuir adsorption isotherm and second order kinetic model with maximum individual adsorption capacities of 67.11, 26.59 and 8.89 mg g −1. The individual and competitive adsorption behaviours indicated that the preference order of adsorption were Pb 2+ > Cu 2+ > Cd 2+ for aluminum oxides, activated carbon, commercial CNTs, and CCNTs as well as other researchers’ CNTs. We suggest that future development of CNTs to combine with metals and/or other materials, such as TiO 2, should consider attached to carriers or surface in order to avoid concerns on environment, health and safety. Thus, growing CNTs on Al 2O 3 particles to form CCNTs is an inherently safe approach for many promising environmental applications.

Effects of Particle Size on Properties of Chemical Reaction Thermodynamics of Nanosystems

In order to study size dependence of the thermodynamic properties of chemical reaction, nanoparticles of diamond were simulated by use of spherical C clusters, the properties of chemical reaction of diamond nanoparticles with different sizes and O_2 were calculated by quantum chemistry method. The results showed that the particle size had obvious effects on the molar standard entropy of reaction, the molar standard enthalpy of reaction, the molar standard Gibbs free energy, and the standard equilibrium constant in heterogeneous reactions; the molar standard entropy of reaction, the molar standard enthalpy of reaction, and the molar standard Gibbs free energy decreased and the standard equilibrium constant increased with the particle diameters of reactants decreasing. These regularities were consistent with experimental results.

Thermodynamics of reactions catalyzed by d-hydantoinase and N-carbamoyl- d-amino acid hydrolase

Microcalorimetry and high-performance liquid chromatography have been used to conduct a thermodynamic investigation of several biochemical reactions catalyzed by the enzymes d-hydantoinase and N-carbamoyl- d-amino acid hydrolase. Values of apparent equilibrium constants K′ and calorimetrically determined molar enthalpies of reaction Δ r H m(cal) were measured for the following d-hydantoinase catalyzed reactions: hydantoin(aq) + H 2O(l) = ureidoacetic acid(aq); 5,6-dihydrouracil(aq) + H 2O(l) = 3-ureidopropanoic acid(aq); 5-phenylhydantoin(aq) + H 2O(l) = 5-phenyl d-carbamoylate(aq); and 5-(4-hydroxyphenyl)hydantoin(aq) + H 2O(l) = 5-(4-hydroxyphenyl) d-carbamoylate(aq). Calorimetric measurements, in which both d-hydantoinase and N-carbamoyl- d-amino acid hydrolase were present, were performed on the following reactions: 5-phenylhydantoin(aq) + 3 H 2O(l) = d-phenylglycine(aq) + carbon dioxide(aq) + ammonia(aq); and (4-hydroxy)-phenylhydantoin(aq) + 3H 2O(l) = d-(4-hydroxyphenyl)glycine(aq) + carbon dioxide(aq) + ammonia(aq). A chemical equilibrium model was then used to calculate thermodynamic property values (equilibrium constants K, standard molar enthalpies of reaction Δ r H m ∘ , standard molar Gibbs free energies of reaction Δ r G m ∘ , and standard molar entropies of reaction Δ r S m ∘ ) for chemical reference reactions that correspond to the overall biochemical reactions that were studied experimentally. In several cases, we also provided estimated property values based on data for structurally similar reactions. The results can be used together with the chemical equilibrium model to calculate values of K′, the standard apparent molar Gibbs free energy change Δ r G m ′ ∘ , the standard apparent molar enthalpy change Δ r H m ′ ∘ , changes in binding of the proton Δ r N(H +), and the position of equilibrium for the several overall biochemical reactions considered in this study over a reasonably wide range of temperature, pH, and ionic strength.

Thermochemistry of rare earth complexes [Ln(Ala)2(Im)(H2O)](ClO4)3 (Ln=Pr, Gd)

The two complexes, [Ln(Ala)2(Im)(H2O)](ClO4)3 (Ln=Pr, Gd), were synthesized and characterized. Using a solution-reaction isoperibol calorimeter, standard enthalpies of reaction of two reactions: LnCl3⋅6H2O(s)+2Ala(s)+Im(s)+3NaClO4(s)=[Ln(Ala)2(Im)(H2O)](ClO4)3(s)+3NaCl(s)+5H2O(l) (Ln=Pr, Gd), at T=298.15 K, were determined to be (39.26±0.10) and (5.33±0.12) kJ mol–1 , respectively. Standard enthalpies of formation of the two complexes at T=298.15 K, ΔfHΘm {[Ln(Ala)2(Im)(H2O)](ClO4)3(s)} (Ln=Pr, Gd), were calculated as –(2424.2±3.3) and –(2443.4±3.3) kJ mol–1 , respectively.

Experimental and ab Initio Study of the HO2·CH3OH Complex: Thermodynamics and Kinetics of Formation

Near-infrared spectroscopy was used to monitor HO2 formed by pulsed laser photolysis of Cl2-O2-CH3OH-N2 mixtures. On the microsecond time scale, [HO2] exhibited a time dependence consistent with a mechanism in which [HO2] approached equilibrium via HO2 + HO2.CH3OH (3, -3). The equilibrium constant for reaction 3, K(p), was measured between 231 and 261 K at 50 and 100 Torr, leading to standard reaction enthalpy and entropy values (1 sigma) of delta(r) = -37.4 +/- 4.8 kJ mol(-1) and delta(r) = -100 +/- 19 J mol(-1) K(-1). The effective bimolecular rate constant, k3, for formation of the HO2.CH3OH complex is .10(-15).exp[(1800 +/- 500)/T] cm3 molecule(-1) s(-1) at 100 Torr (1 sigma). Ab initio calculations of the optimized structure and energetics of the HO2.CH3OH complex were performed at the CCSD(T)/6-311++G(3df,3pd)//MP2(full)/6-311++G(2df,2pd) level. The complex was found to have a strong hydrogen bond (D(e) = 43.9 kJ mol(-1)) with the hydrogen in HO2 binding to the oxygen in CH3OH. The calculated enthalpy for association is delta(r) = -36.8 kJ mol(-1). The potentials for the torsion about the O2-H bond and for the hydrogen-bond stretch were computed and 1D vibrational levels determined. After explicitly accounting for these degrees of freedom, the calculated Third Law entropy of association is delta(r) = -106 J mol(-1) K(-1). Both the calculated enthalpy and entropy of association are in reasonably good agreement with experiment. When combined with results from our previous study (Christensen et al. Geophys. Res. Lett. 2002, 29; doi:10.1029/2001GL014525), the rate coefficient for the reaction of HO2 with the complex, HO2 + HO2.CH3OH, is determined to be (2.1 +/- 0.7) x 10(-11) cm3 molecule(-1) s(-1). The results of the present work argue for a reinterpretation of the recent measurement of the HO2 self-reaction rate constant by Stone and Rowley (Phys. Chem. Chem. Phys. 2005, 7, 2156). Significant complex concentrations are present at the high methanol concentrations used in that work and lead to a nonlinear methanol dependence of the apparent rate constant. This nonlinearity introduces substantial uncertainty in the extrapolation to zero methanol.

Rate and Equilibrium Constant of the Reaction of 1-Methylvinoxy Radicals with O2: CH3COCH2 + O2 ↔ CH3COCH2O2

The reaction of 1-methylvinoxy radicals, CH3COCH2, with molecular oxygen has been investigated by experimental and theoretical methods as a function of temperature (291-520 K) and pressure (0.042-10 bar He). Experiments have been performed by laser photolysis coupled to a detection of 1-methylvinoxy radicals by laser-induced fluorescence LIF. The potential energy surface calculations were performed using ab inito molecular orbital theory at the G3MP2B3 and CBSQB3 level of theory based on the density function theory optimized geometries. Derived molecular properties of the characteristic points of the potential energy surface were used to describe the mechanism and kinetics of the reaction under investigation. At 295 K, no pressure dependence of the rate constant for the association reaction has been observed: k(1,298K) = (1.18 +/- 0.04) x 10(-12) cm3 s(-1). Biexponential decays have been observed in the temperature range 459-520 K and have been interpreted as an equilibrium reaction. The temperature-dependent equilibrium constants have been extracted from these decays and a standard reaction enthalpy of deltaH(r,298K) = -105.0 +/- 2.0 kJ mol(-1) and entropy of deltaS(r,298K) = -143.0 +/- 4.0 J mol(-1) K(-1) were derived, in excellent agreement with the theoretical results. Consistent heats of formation for the vinoxy and the 1-methylvinoxy radical as well as their O2 adducts are recommended based on our complementary experimental and theoretical study deltaH(f,298K) = 13.0 +/- 2.0, -32. 9+/- 2.0, -85.9 +/- 4.0, and -142.1 +/- 4.0 kJ mol(-1) for CH2CHO, CH3COCH2 radicals, and their adducts, respectively.

Fabrication of TiSi2 Using Microwave Hydrogen Plasma Annealing

A new method, microwave hydrogen plasma annealing of sputter-deposited titanium films on an Si (111) substrate, was used to fabricate TiSi2 films. The films were characterized by x-ray diffraction, Auger electron spectroscopy, sputter depth profiling, and four-point probe resistivity measurements. Polycrystalline TiSi2, dominated by components with (040) orientation, was grown at the annealing temperature of 800 °C. The microwave hydrogen plasma was considered not only to provide the heat for the solid-phase reaction, but also to promote the solid-phase reaction by enhancing atom mobility and diffusion.

Multilayer Formulation of the Fragment Molecular Orbital Method (FMO)

The fragment molecular orbital method (FMO) has been generalized to allow for multilayer structure. Fragments are assigned to layers, and each layer can be described with a different basis set and/or level of electron correlation. Interlayer boundaries are treated in the general spirit of the FMO method since they also coincide with some interfragment boundaries. The question of the one- and two-layer FMO accuracy dependence upon the fragmentation scheme is also addressed. The new method has been applied to predict the reaction barrier and the reaction heat for the Diels-Alder reaction with a representative set of reactants based on dividing fragments in two layers. The 6-31G* basis set has been used for the active site and the 6-31G*, 6-31G, 3-21G, and STO-3G basis sets have been used for the substituents. Different levels of electron correlation (RHF, B3LYP, and MP2) have been applied to layers in systematic fashion. The one-layer FMO errors in the reaction barrier and the reaction heat were 2.0 kcal/mol or less for all levels applied (RHF, B3LYP, and MP2), relative to full ab initio methods. For the two-layer method the error was found to be several kcal/mol. Benchmark calculations of the activation barrier for the decarboxylation of phenylcyanoacetate by beta-cyclodextrin demonstrated that the two-layer calculations are efficient, being 36 times faster than the regular DFT, as well as accurate, with the error being 1.0 kcal/mol.

Saturation molalities and standard molar enthalpies of solution of 2′-deoxyadenosine · H 2O(cr), 2′-deoxycytidine · H 2O(cr), 2′-deoxyguanosine · H 2O(cr), 2′-deoxyinosine(cr), and 2′-deoxyuridine(cr) in H 2O(l)

Saturation molalities m(sat) in H 2O(l) have been measured for the substances 2′-deoxyadenosine · H 2O(cr), 2′-deoxycytidine · H 2O(cr), 2′-deoxyguanosine · H 2O(cr), 2′-deoxyinosine(cr), and 2′-deoxyuridine(cr) by using h.p.l.c. The states of hydration were established by performing Karl Fischer analyses on samples of these substances, which had been allowed to equilibrate with their respective aqueous saturated solutions for several days at T ≈ 298 K and then dried with air at T ≈ 296 K for ≈24 h. The crystalline forms of the substances were identified by comparison of the results of X-ray diffraction measurements with results from the literature. Also, calorimetric molar enthalpies of solution Δ sol H m(cal) for these substances were measured by using an isoperibol solution calorimeter. A self-association (stacking) model was used to estimate values of the activity coefficients γ and relative apparent molar enthalpies L ϕ for these substances. These γ and L ϕ values were used to adjust the measured values of m(sat) and Δ sol H m to the standard state and thus obtain values of the standard molar Gibbs free energy Δ sol G m ∘ and enthalpy changes Δ sol H m ∘ for the dissolution reactions of these substances. The values of the p Ks and of the standard molar enthalpies of the ionization reactions were also used to account for speciation of the substances in the calculations of Δ sol G m ∘ and Δ sol H m ∘ .