Curves Of Reactions Research Articles

Representation of “Broad” Falloff Curves for Dissociation and Recombination Reactions

Abstract Expressions for representing the pressure dependence of unimolecular dissociation and the reverse recombination reactions are compared. Situations are considered where the broadening of the corresponding falloff curves is particularly pronounced, i.e. where broadening factors at the center of the falloff curves, F cent, are very small and falloff curves correspondingly become very “broad”. Such situations arise when unimolecular reactions of molecules with large numbers of low-frequency modes and high-temperature situations are considered. Recombination reactions of polyatomic species in atmospheric chemistry and dissociation reactions of large molecules in combustion are the fields of application of the present results. While previously proposed expressions for asymmetric broadening factors showed artifacts when F cent decreased to values below about 0.4, alternative functions are described which avoid these problems for situations where F cent decreases to values far below 0.1.

Theoretical prediction on low-lying states of HAlP and HPAl radicals

The HAlP and HPAl radicals have been studied using CASSCF, CASPT2, and CCSD(T) methods. The geometries of the stationary points were optimized at the CASPT2/ANO and CCSD(T)/aug-cc-pVTZ levels. For the double states, the potential energy curves of isomerization reactions between HAlP and HPAl were calculated as functions of HAlP bond angle. The calculated results showed that the ground-state HAlP is linear, while the ground-state HPAl is bent, which is in contradiction to Walsh’s rules predicting linear structures for the HXY systems containing 10 or less valence electrons. Some quartet states of HAlP and HPAl were also calculated.

THEORETICAL STUDY ONHBeP-ANDHPBe-ANIONS USING MULTICONFIGURATION SECOND-ORDER PERTURBATION THEORY

Some low-lying states of the nine-valence-electron systems HBeP-and HPBe-anions have been studied for the first time using three methods CASSCF, CASPT2 and B3LYP with the contracted atomic natural orbital (ANO) and cc-pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO, CASPT2/ANO and B3LYP/cc-pVTZ levels. The potential energy curves of isomerization reactions between HBeP-and HPBe-were calculated as a function of HBeP bond angle. The ground and the first excited states of HBeP-are predicted to be X2Π and A2Σ+states, respectively. The X2Σ+and A2Π states of the linear HPBe-are both first-order saddle points because they have unique imaginary frequency. Two bent minima M1 and M2 were found along the 12A′ and 12A″ potential energy surfaces, respectively. The calculated results indicated that the ground-state HBeP-is linear, while the ground-state HPBe-is bent.

Theoretical prediction on low-lying states of HBP and HPB radicals

Some low-lying states of the nine-valence-electron systems HBP and HPB radicals have been studied using three methods CASSCF, CASPT2, and B3LYP with the contracted atomic natural orbital (ANO) and cc-pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO, CASPT2/ANO, and B3LYP/cc-pVTZ levels. The potential energy curves of isomerization reactions between HBP and HPB were calculated as a function of HBP bond angle. The calculated results indicated that the ground-state HBP is linear, while the ground-state HPB is bent, which is in contradiction to Walsh’s rules predicting linear structures for the HXY systems containing 10 or less valency electrons.

Kinetic chemiluminescence as a method for study of free radical reactions

The review gives concepts of analysis of kinetics of complex reactions with the participation of free-radicals. The concepts are based on the comparison of the kinetic curves of the chemiluminescent reactions in the presence of a physical enhancer coumarin C-525 with the simulated kinetic functions. This method was applied to the investigation of the mechanism of a branched-chain reaction of lipid peroxidation in biological and phospholipid membranes as well as to the effect of antioxidants and determination of their activities. It was also used for studying the reaction of the formation of free radicals in the complex of cytochrome c with cardiolipin. This reaction plays a key role in the initiation of apoptosis.

CASPT2 study on low-lying states of HBS+ and HSB+ cations

Some low-lying states of the nine-valence-electron systems HBS+ and HSB+ cations have been studied by large-scale theoretical calculations using three methods CASSCF, CASPT2, and DFT B3LYP with the contracted atomic natural orbital and cc-pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces were optimized and the energies were calculated. The potential energy curves of isomerization reactions between HBS+ and HSB+ were calculated as a function of HBS bond angle. The calculated results indicated that the ground-state HBS+ is linear, while the ground-state HSB+ is bent, which is in contradiction to Walsh's rules predicting linear structures for the HXY systems containing 10 or less valency electrons.

Theoretical prediction on HAlS+ and HSAl+ cations using multiconfiguration second‐order perturbation theory

AbstractSome low‐lying states of the HAlS+ and HSAl+ cations have been studied for the first time by large‐scale theoretical calculations using three methods: complete active space self‐consistent field (CASSCF), complete active second‐order perturbation theory (CASPT2), and density functional theory Becke's three‐parameter hybrid function with the nonlocal correlation of Lee–Yang–Parr (B3LYP) with the contracted atomic natural orbital (ANO‐L) and cc‐pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces (PESs) were optimized at the CASSCF/ANO‐L and B3LYP/cc‐pVTZ levels. The ground and the first excited states of linear HAlS+ are predicted to be X2Π and A2Σ+ states, respectively. For the linear HSAl+ structure, the first excited state is A2Σ+. The X2Π state of linear HSAl+ is a second‐order saddle point, because it has two imaginary frequencies. Two bent global minima M1 and M2 were found along the 12A′ and 12A″ PESs, respectively. The CASPT2/ANO‐L potential energy curves of isomerization reactions were calculated as a function of HAlS bond angle. According to our calculations, the ground‐state HAlS+ is linear, whereas the ground‐state HSAl+ is bent. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Theoretical calculations of the reaction cross-sections for proton-induced reactions on natural copper using ALICE-IPPE code

A theoretical study of the nuclear-reaction cross sections for proton-induced reactions on (63)Cu and (65)Cu was performed in the proton energy range from threshold values up to 50MeV. The produced nuclei were different isotopes of Zn, Cu, Ni, Co and Mn, some of which have important applications. The reaction cross-section calculations were performed using the ALICE-IPPE code, which depends on the pre-equilibrium compound nucleus model. This code is suitable for the studied energy and isotopic mass ranges. Approximately 14 excitation functions for the different reactions have been constructed from the calculated cross-section values. The excitation function curves for the proton reactions with natural copper targets have been constructed from those for enriched targets using the natural abundance of the copper isotopes. Comparisons between the calculated excitation functions with those previously experimentally measured are given whenever the experimental values were available. Some statistical parameters were introduced to control the quality of the fitting between both the experimental and the theoretical calculated cross-section values.

Applications of the IAPWS-95 formulation in fluid inclusion and mineral-fluid phase equilibria

The IAPWS-95 formulation explicit in Helmholtz free energy proposed by Wagner and Pruβ (2002) is the best equation of state of water, from which all thermodynamic properties can be obtained over a wide T– p range from 273.16 to 1273 K and from 0 to 1000 MPa with experimental accuracy. This paper reports the applications of the IAPWS-95 formulation in fluid inclusion and mineral-water phase equilibria. A reliable and highly efficient calculation method is presented for the saturated properties of water so that the formulation can be conveniently applied in the study of fluid inclusion, such as calculating homogenization pressures, homogenization densities (or molar volumes), volume fractions and isochores. Meanwhile, the univariant curves of some mineral-dehydration reactions are calculated based on the IAPWS-95 formulation. The computer code of the IAPWS-95 formulation can be obtained from the corresponding author.

Revisiting falloff curves of thermal unimolecular reactions

Master equations for thermal unimolecular reactions and the reverse thermal recombination reactions are solved for a series of model reaction systems and evaluated with respect to broadening factors. It is shown that weak collision center broadening factors F(cent) (wc) can approximately be related to the collision efficiencies β(c) through a relation F(cent) (wc) ≈ max {β(c) (0.14), 0.64(±0.03)}. In addition, it is investigated to what extent weak collision falloff curves in general can be expressed by the limiting low and high pressure rate coefficients together with central broadening factors F(cent) only. It is shown that there cannot be one "best" analytical expression for broadening factors F(x) as a function of the reduced pressure scale x = k(0)∕k(∞). Instead, modelled falloff curves of various reaction systems, for given k(0), k(∞), and F(cent), fall into a band of about 10% width in F(x). A series of analytical expressions for F(x), from simple symmetric to more elaborate asymmetric broadening factors, are compared and shown to reproduce the band of modelled broadening factors with satisfactory accuracy.

The Importance of NO+(H2O)4 in the Conversion of NO+(H2O)n to H3O+(H2O)n: I. Kinetics Measurements and Statistical Rate Modeling

The kinetics for conversion of NO(+)(H(2)O)(n) to H(3)O(+)(H(2)O)(n) has been investigated as a function of temperature from 150 to 400 K. In contrast to previous studies, which show that the conversion goes completely through a reaction of NO(+)(H(2)O)(3), the present results show that NO(+)(H(2)O)(4) plays an increasing role in the conversion as the temperature is lowered. Rate constants are derived for the clustering of H(2)O to NO(+)(H(2)O)(1-3) and the reactions of NO(+)(H(2)O)(3,4) with H(2)O to form H(3)O(+)(H(2)O)(2,3), respectively. In addition, thermal dissociation of NO(+)(H(2)O)(4) to lose HNO(2) was also found to be important. The rate constants for the clustering increase substantially with the lowering of the temperature. Flux calculations show that NO(+)(H(2)O)(4) accounts for over 99% of the conversion at 150 K and even 20% at 300 K, although it is too small to be detectable. The experimental data are complimented by modeling of the falloff curves for the clustering reactions. The modeling shows that, for many of the conditions, the data correspond to the falloff regime of third body association.

CASPT2 study on low‐lying states of HMgO and HOMg

AbstractThe HMgO and magnesium monohydroxide (HOMg) have been reinvestigated using the complete active space self‐consistent field (CASSCF) and multiconfiguration second‐order perturbation theory (CASPT2) methods with the contracted atomic natural orbital (ANO) basis sets. The geometries of all stationary points along the potential energy surfaces (PESs) were optimized at the CASSCF/ANO levels. The ground and the first excited states of HMgO are predicted to be X2Π and A2Σ+ states, respectively. It was predicted that the ground state of HOMg is X2Σ+ state. The A2Π state of HOMg has unique imaginary frequency. A bent local minimum M1 was found for the first time along the 12A″ PES and the A2Π state of HOMg should be the transition state of the isomerization reactions for M1 ↔ M1. The CASPT2/ANO potential energy curves of isomerization reactions were calculated as a function of HMgO bond angle. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012

Theoretical study on low-lying states of HAlO+ and HOAl+ cations

Some low-lying states of HAlO+ and HOAl+ cations have been studied using the complete-active-space self-consistent field (CASSCF) and multiconfiguration second-order perturbation theory (CASPT2) methods with the contracted atomic natural orbital (ANO) basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO and CASPT2/ANO levels. The ground and the first excited states of HAlO+ are predicted to be X2Π and A2Σ+ states, respectively. It was predicted that the ground state of HOAl+ is X2Σ+ state. The A2Π state of HOAl+ has unique imaginary frequency. A bent local minimum M1 was found along the 12A″ potential energy surface, and the A2Π state of HOAl+ should be the transition state of the isomerization reactions for M1 ↔ M1. The CASPT2/ANO potential energy curves of isomerization reactions were calculated as a function of HAlO bond angle. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

Optical fluid and biomolecule transport with thermal fields

A long standing goal is the direct optical control of biomolecules and water for applications ranging from microfluidics over biomolecule detection to non-equilibrium biophysics. Thermal forces originating from optically applied, dynamic microscale temperature gradients have shown to possess great potential to reach this goal. It was demonstrated that laser heating by a few Kelvin can generate and guide water flow on the micrometre scale in bulk fluid, gel matrices or ice without requiring any lithographic structuring. Biomolecules on the other hand can be transported by thermal gradients, a mechanism termed thermophoresis, thermal diffusion or Soret effect. This molecule transport is the subject of current research, however it can be used to both characterize biomolecules and to record binding curves of important biological binding reactions, even in their native matrix of blood serum. Interestingly, thermophoresis can be easily combined with the optothermal fluid control. As a result, molecule traps can be created in a variety of geometries, enabling the trapping of small biomolecules, like for example very short DNA molecules. The combination with DNA replication from thermal convection allows us to approach molecular evolution with concurrent replication and selection processes inside a single chamber: replication is driven by thermal convection and selection by the concurrent accumulation of the DNA molecules. From the short but intense history of applying thermal fields to control fluid flow and biological molecules, we infer that many unexpected and highly synergistic effects and applications are likely to be explored in the future.

CASPT2 study on low-lying states of HBN and HNB radicals

In this study, some low-lying states of the HBN and HNB radicals have been studied using multiconfiguration second-order perturbation theory. The geometries of all stationary points along the potential energy surfaces (PESs) were optimized at the CASPT2/cc-pVQZ level. The ground and the first excited states of HBN were predicted to be X2Π and A2Σ+ states, respectively. It was predicted that the ground state of HNB is X2Σ+ state. The A2Π state of HNB has unique imaginary frequency, which was different from the previously published results. A bending local minimum M1 was found for the first time along the 12A″ PES, and the A2Π state of HNB should be the transition state of the isomerization reactions for M1 M1. The CASPT2/ANO potential energy curves (PECs) of isomerization reactions for HBN HNB were calculated as a function of HBN bond angle. By comparing the CASPT2 and CASSCF calculated results, we concluded that the influence of the dynamic electron correlation on HBN HNB system is not large. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2011

A fitting formula for the falloff curves of unimolecular reactions, II: Tunneling effects

AbstractBy taking into account effects of tunneling on the shape of the falloff curves of unimolecular reaction rate constants based on Troe's weak collision integral, a fitting formula for these curves is developed and then examined for several tunneling‐affected reactions. It is demonstrated that, compared to the widely used Troe's formula, the present expression not only substantially enhances the accuracy in fitting for tunneling‐affected reactions, but it is also computationally more efficient in its evaluation. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 43: 31–42, 2011

Role of additives in LiBH 4–MgH 2 reactive hydride composites for sorption kinetics

The influence of additives on the reaction kinetics and microstructure refinement in LiBH 4–MgH 2 composites is investigated in detail. Indications of the rate-limiting processes during the reactions are obtained by comparison of the measured reaction kinetics with simulations with one specific rate-limiting process. The kinetics of the sorption reactions are derived from volumetric measurements as well as from in situ X-ray diffraction measurements. During desorption, the hydrogen is released at a constant rate, which is possibly correlated with the one-dimensional growth of MgB 2 platelets. In contrast, the kinetic curves of the absorption reactions exhibit the typical shape of contracting-volume controlled kinetics. The microscopical interpretation of kinetic measurements are supported by transmission electron microscopy images confirming the formation of additive-nanostructures in the grain boundaries upon cycling. The present investigations underline the importance of the additives as nucleation substrates and the influence of microstructure on the reaction kinetics.

Multifunctional Antioxidant Activities of Alkyl Gallates

A series (C 1 to C 16 ) of alkyl gallates was tested for their antioxidant activity for food protection and human health. One molecule of alkyl gallate, regardless of alkyl chain length, scavenges six molecules of 1,1-diphenyl-2- picrylhydrazyl (DPPH). Alkyl gallates inhibited the linoleic acid peroxidation catalyzed by soybean lipoxygenase-1 (EC 1.13.11.12, Type 1) without being oxidized. The progress curves for enzyme reactions were recorded by both spectropho- tometric and polarographic methods and the inhibitory activity was a parabolic function of their lipophilicity (log P) and maximized with alkyl chain length between C 12 and C 16 . Tetradecanyl (C 14 ) gallate exhibited the most potent inhibition with an IC 50 of 0.06 µM. The inhibition kinetics of dodecyl gallate (C 12 ) revealed competitive and slow-binding inhibi- tion. Alkyl gallates chelate transition metal ions and this chelation ability should be of considerable advantage as antioxi- dants. Additionally, gallic acid was found to inhibit superoxide anion generated by xanthine oxidase (EC 1.1.3.22) but did not inhibit enzymatically catalyzed uric acid formation.

Theoretical study on HBO+ and HOB+ cations using multiconfiguration second‐order perturbation theory

The HBO(+) and HOB(+) cations have been reinvestigated using the CASSCF and CASPT2 methods in conjunction with the contracted atomic natural orbital (ANO) basis sets. The geometries of all stationary points in the potential energy surfaces were optimized at the CASSCF/ANO and CASPT2/ANO levels. The ground and the first excited states of HBO(+) are predicted to be X(2)Pi and A(2)Sigma(+) states, respectively. It was predicted that the ground state of HOB(+) is X(2)Sigma(+) state. The A(2)Pi state of HOB(+) has unique imaginary frequency. A bending local minimum M1 was found for the first time along the 1(2)A'' potential energy surface and the A(2)Pi state of HOB(+) should be the transition state of the isomerization reactions for M1<--> M1. The CASPT2/ANO potential energy curves (PECs) of isomerization reactions were calculated as functions of the HBO bond angle. Many of the CASSCF and CASPT2 calculated results were different from the previously published QCISD(T) results.

Theoretical prediction on HBeN− and HNBe− anions using multiconfiguration second-order perturbation theory

The HBeN− and HNBe− anions have been investigated for the first time using the CASSCF, CASPT2, and DFT/B3LYP methods with the contracted atomic natural orbital (ANO) and cc-pVTZ basis sets. The geometries of all stationary points along the potential energy surfaces were optimized at the CASSCF/ANO and B3LYP/cc-pVTZ levels. The ground and the first excited states of HBeN− are predicted to be X2Π and A2Σ+ states, respectively. It was predicted that the ground state of HNBe− is X2Σ+ state. The A2Π state of HNBe− has unique imaginary frequency. A bend local minimum M1 was found along the 12A″ potential energy surface and the A2Π state of HNBe− should be the transition state of the isomerization reactions for M1 ↔ M1. The CASPT2/ANO potential energy curves of isomerization reactions were calculated as a function of HBeN bond angle. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010