Chemical Kinetic Studies Research Articles

Preparation and sorption behavior of DEAE-cellulose-thiourea-glutaraldehyde sorbent for Pt(IV) and Pd(II) from leaching solutions

This work investigates the adsorption behavior of Diethylaminoethyl-cellulose-thiourea-glutaraldehyde (DEAE-C/TU/GA) sorbent, which was synthesized through the reaction of crosslinking of glutaraldehyde using thiourea for platinum (Pt(IV)) and palladium (Pd(II)) ions from leaching solutions. The effects of pH and adsorption parameters, such as the sorbent dosage, contact time, temperature, and adsorption isotherms, were studied. Furthermore, chemical adsorption kinetic studies for adsorptions of these metal ions were carried out. The adsorption equilibrium data were fit better using the Langmuir model than the Freundlich model. The activation energies (Ea) of Pt(IV) and Pd(II) were 77.70 and 23.03 kJ/mol, respectively. The best desorption reagent was 1.0M HCl–1.0M TU solution for both Pd(II) and Pt(IV), which could remove more than 85% of the Pt(IV) and Pd(II) in the fourth adsorption–desorption cycle.

Probing combustion chemistry in a miniature shock tube with synchrotron VUV photo ionization mass spectrometry.

Tunable synchrotron-sourced photoionization time-of-flight mass spectrometry (PI-TOF-MS) is an important technique in combustion chemistry, complementing lab-scale electron impact and laser photoionization studies for a wide variety of reactors, typically at low pressure. For high-temperature and high-pressure chemical kinetics studies, the shock tube is the reactor of choice. Extending the benefits of shock tube/TOF-MS research to include synchrotron sourced PI-TOF-MS required a radical reconception of the shock tube. An automated, miniature, high-repetition-rate shock tube was developed and can be used to study high-pressure reactive systems (T > 600 K, P < 100 bar) behind reflected shock waves. In this paper, we present results of a PI-TOF-MS study at the Advanced Light Source at Lawrence Berkeley National Laboratory. Dimethyl ether pyrolysis (2% CH3OCH3/Ar) was observed behind the reflected shock (1400 < T5 < 1700 K, 3 < P5 < 16 bar) with ionization energies between 10 and 13 eV. Individual experiments have extremely low signal levels. However, product species and radical intermediates are well-resolved when averaging over hundreds of shots, which is ordinarily impractical in conventional shock tube studies. The signal levels attained and data throughput rates with this technique are comparable to those with other synchrotron-based PI-TOF-MS reactors, and it is anticipated that this high pressure technique will greatly complement those lower pressure techniques.

Influence of the double bond on the hydrogen abstraction reactions of methyl esters with hydrogen radical: an ab initio and chemical kinetic study

This work reports a systematic ab initio and chemical kinetic study of the rate constants for hydrogen atom abstraction reactions by hydrogen radical on the isomers of unsaturated C6 methyl esters.

Theoretical chemical kinetic study of the H-atom abstraction reactions from aldehydes and acids by Ḣ atoms and ȮH, HȮ2, and ĊH3 radicals.

We have performed a systematic, theoretical chemical kinetic investigation of H atom abstraction by Ḣ atoms and ȮH, HȮ2, and ĊH3 radicals from aldehydes (methanal, ethanal, propanal, and isobutanal) and acids (methanoic acid, ethanoic acid, propanoic acid, and isobutanoic acid). The geometry optimizations and frequencies of all of the species in the reaction mechanisms of the title reactions were calculated using the MP2 method and the 6-311G(d,p) basis set. The one-dimensional hindered rotor treatment for reactants and transition states and the intrinsic reaction coordinate calculations were also determined at the MP2/6-311G(d,p) level of theory. For the reactions of methanal and methanoic acid with Ḣ atoms and ȮH, HȮ2, and ĊH3 radicals, the calculated relative electronic energies were obtained with the CCSD(T)/cc-pVXZ (where X = D, T, and Q) method and were extrapolated to the complete basis set limit. The electronic energies obtained with the CCSD(T)/cc-pVTZ method were benchmarked against the CCSD(T)/CBS energies and were found to be within 1 kcal mol(-1) of one another. Thus, the energies calculated using the less expensive CCSD(T)/cc-pVTZ method were used in all of the reaction mechanisms and in calculating our high-pressure limit rate constants for the title reactions. Rate constants were calculated using conventional transition state theory with an asymmetric Eckart tunneling correction, as implemented in Variflex. Herein, we report the individual and average rate constants, on a per H atom basis, and total rate constants in the temperature range 500-2000 K. We have compared some of our rate constant results to available experimental and theoretical data, and our results are generally in good agreement.

Chemical Kinetic Studies on Polyurethane Formation of GAP and HTPB with IPDI by Using &lt;i&gt;In Situ&lt;/i&gt; FT-IR Spectroscopy

The high-performance solid propellants play very important role in defense industry, which required highly energetic binders with good mechanical properties. In order to get the activation parameters for energetic binders, In-Situ FT-IR spectroscopic technique is used to study the chemical kinetics of glycidyl azide polymer (GAP) and hydroxyl terminated poly butadiene (HTPB) with isophorone diisocyanate (IPDI) at various temperatures. The reaction was followed by monitoring the change in intensity of the absorption band of NCO stretching at 2257cm-1 and CO stretching at 1731cm-1. The polyurethane reaction has been found to be second order and the rate constant seems to be different between GAP/IPDI and HTPB/IPDI due to reactivity difference of OH groups. Dibutyl tin dilurate (DBTDL) was used as curing catalyst. By using Arrhenius and Eyring equations, the activation parameters were obtained at different temperatures (60, 70, 80 and 90°C). The apparent activation energy for the two systems GAP/IPDI and HTPB/IPDI were found to be 63.51 kJ mol-1 and 41.06 kJ mol-1 while the enthalpy and entropy of activation were found to be 62.35 kJ mol-1 and-36.24 kJ.mol-1K-1, 39.08 J mol-1 and-98.84 J mol-1K-1 respectively.Key words: In-Situ FT-IR; glycidyl azide polymer (GAP); hydroxyl terminated poly butadiene (HTPB); chemical kinetics; polyurethane; dibutyl tin dilurate (DBTDL).

Macroscopic, thermodynamic, kinetic and microscopic study of nitric acid pickling of Elektron 21 (EV31A) magnesium alloy

The study of pickling of the EL21T6 substrate in a nitric acid bath firstly provided knowledge of the influence of the different experimental parameters (concentration of acid, temperature and stirring of the solution) in relation to the etching rate. This experimental part led to the choice of standard pickling (Tbath = 25 °C, moderate stirring (250 rpm), [HNO3] = 1.20 mol/L, duration of 2 min) so as to obtain constant removal of material, even after several uses of the pickling bath. SEM observations also confirmed that in these operating conditions, pickling concerns both the grains of the matrix and the precipitates of type Mg3(Nd, Gd), leading to uniform removal of material from the surface. Working from a number of assumptions, thermodynamic and chemical kinetic studies then allowed a pickling mechanism to be proposed and led to obtaining values for the corresponding kinetic parameters (order of reaction, constant of mean rate, activation energy) to be obtained.

Experimental and chemical kinetic study of CO and NO formation in oxy-methane premixed laminar flames doped with NH3

The present work focuses on the oxy-fuel combustion of methane doped with ammonia in a premixed laminar burner operating at atmospheric pressure, and includes both experiments and a chemical kinetic study. CO and NO formation/emission were examined as a function of the stoichiometry and oxidizer composition. The experimental results showed that, for all oxidizer compositions studied, an increase in the excess oxygen coefficient generally decreases both the CO and NO emissions. Moreover, for the O2/CO2 environments, decreasing the oxygen concentration in the oxidizer, for a given excess oxygen coefficient, leads to higher CO emissions, but lower NO emissions. In air firing, the CO emissions were found to be significantly lower than those measured under oxy-fuel conditions, while the NO emissions were higher than those from the oxy-fuel cases. The chemical kinetic study allowed to identify the main reactions that directly (with the aid of a rate-of-production analysis) and indirectly (through a sensitivity analysis) influence both the CO and NO emissions. Under oxy-fuel conditions, CO2+H↔CO+OH and 1CH2+CO2↔CH2O+CO significantly contribute to CO formation additionally to those reactions found in air-fired combustion, while CO oxidation takes place through CO+OH↔CO2+H for all studied conditions. Formation of NO occurs for all conditions mainly with HNO as intermediate, particularly through HNO+H↔H2+NO. Once NO is formed, interconversion to NO2 occurs.

Influences of Cylinder Wall Temperature on Heat Release during Compression Period

Compression period in a diesel engine is generally seen as initial characteristics before injection into combustion chamber. A free-piston type rapid compression machine (RCM) has been designed simulate the combustion phenomena in order to observe the chemical and physical kinetics studies at elevated pressures and temperatures. Purpose of this study is to clarify the effects of wall cylinder temperature on air heat release, especially during compression period. This method can a light piston is pneumatically shot and gets hammered in stopper at compression end. Measurements were made on a light piston compress in a rapid compression machine (RCM) with intended to simulate the actual compression period related phenomena. During this phenomena, the ambient temperature influences from the cylinder wall temperature has appear beneficial for the biodiesel fuel premixing and achieving best mixture preparation There are three tests will used to investigate the effects of the variant temperature of wall cylinder during compression period. Results show high temperature on cylinder wall will be effects decrease during temperature drop after compression stroke. The new characteristics rapid compression machine (RCM) is to develop and analyse before combustion process.

Theoretical and kinetic study of the hydrogen atom abstraction reactions of ethyl esters with hydrogen radicals

Ab initio and chemical kinetic study of the hydrogen abstraction reactions by the hydrogen radical on ethyl formate, ethyl acetate, ethyl propanoate, and ethyl butanoate have been performed at the CCSD(T)/CBS//B3LYP/6-311G(d, p) level of theory. High-pressure limit rate constants at temperatures from 300 to 2500K have been calculated for all of the reaction channels using transition state theory with Eckart tunneling corrections, and the data are fitted to the modified three parameters Arrhenius expression using least-squares regression. A branching ratio analysis for each reaction site has also been investigated for all of the ethyl esters.

Double-focusing mixing jet for XFEL study of chemical kinetics.

Several liquid sample injection methods have been developed to satisfy the requirements for serial femtosecond X-ray nanocrystallography, which enables radiation-damage-free determination of molecular structure at room temperature. Time-resolved nanocrystallography would combine structure analysis with chemical kinetics by determining the structures of the transient states and chemical kinetic mechanisms simultaneously. A windowless liquid mixing jet device has been designed for this purpose. It achieves fast uniform mixing of substrates and enzymes in the jet within 250 µs, with an adjustable delay between mixing and probing by the X-ray free-electron laser beam of up to 1 s for each frame of a `movie'. The principle of the liquid mixing jet device is illustrated using numerical simulation, and experimental results are presented using a fluorescent dye.

A scanned-wavelength-modulation absorption-spectroscopy sensor for temperature and H2O in low-pressure flames

The design and demonstration of a tunable diode laser sensor for in situ temperature and water (H2O) measurements in laboratory flames is presented. A newly-designed probe consisting of two single-crystal sapphire rods is used to guide 2.9 μm laser light across the core of a flame while avoiding absorption by water outside of the flame. The sensor probes two H2O transitions near 2.9 μm using a scanned-wavelength-modulation absorption-spectroscopy spectral-fitting technique, which enables measurements without calibration or knowledge of the mixture collisional-broadening coefficient. To demonstrate the sensor, temperature and water mole fraction measurements were acquired in stoichiometric, burner-stabilized flames of methane/oxygen/argon at pressures of 25 Torr and 60 Torr. Typical total uncertainties in the temperature and water mole fraction measurements were ±50 K and ±0.016, respectively. This sensor is simple, robust and accurate and enables improved chemical kinetics studies of low-pressure flames. Improvements to reduce temperature and H2O precision to ±20 K and ±0.008, respectively, are discussed.

Reflections on my career as a marine physical chemist, and tales of the deep.

This is a personal review of how one can apply the principles of physical chemistry to study the ocean and other natural waters. Physical chemistry is the study of chemical thermodynamics, kinetics, and molecular structure. My long-term interest in the chemistry of seawater is an extension of my early work on water and the interactions that occur in aqueous electrolyte solutions, which I began as part of my PhD research on the thermodynamics of organic acids in water. Over the years, I have attempted to apply the tools of physical chemistry to elucidate the structures of seawater, brines, lakes, and rivers. I have developed and continue to work on ionic interaction models that can be applied to all natural waters. Here, I reflect on how my students, postdocs, research assistants, and scientific colleagues have influenced my life, my career, and the field of marine physical chemistry. My hope was and is to use these tools to understand the molecular structures of natural waters.

A molecular dynamics simulation of hydrogen atoms collisions on an H-preadsorbed silica surface

The interaction of hydrogen atoms and molecules with a silica surface is relevant for many research and technological areas. Here, the dynamics of hydrogen atoms colliding with an H-preadsorbed β-cristobalite (0 0 1) surface has been studied using a semiclassical collisional method in conjunction with a recently developed analytical potential energy surface based on density functional theory (DFT) calculations. The atomic recombination probability via an Eley–Rideal (E–R) mechanism, as well as the probabilities for other competitive surface processes, have been determined in a broad range of collision energies (0.04–3.0 eV) for off-normal (θv = 45°) and normal (θv = 0°) incidence and for two different surface temperatures (TS = 300 and 1000 K). H2,gas molecules form in roto-vibrational excited levels while the energy transferred to the solid surface is below 10% for all simulated conditions. Finally, the global atomic recombination coefficient (γE–R) and vibrational state resolved recombination coefficients (γ(v)) were calculated and compared with the available experimental values. The calculated collisional data are of interest in chemical kinetics studies and fluid dynamics simulations of silica surface processes in H-based low-temperature, low-pressure plasmas.

Multiplexed time- and photon-energy-resolved photoionization mass spectrometer for kinetics of radical reactions study

A combination of flash photolysis reactor tube and synchrotron radiation photoionization mass spectrometer has been constructed for the study of the gas phase chemical kinetics. The radical-molecule chemical reactions in a side-sampled flow tubular reactor are initiated by a pulsed photolysis laser. Then the gas mixture is sampled via a pinpole and photoionized by tunable synchrotron radiation VUV photons. The constant flux ions are detected by the subsequent time-of-flight mass spectrometer. At the same time, pulsed generator generates a burst of pulses with duration of 40-50 s, which initiate the collection of mass spectrometer. The continuous collection covers the overall reaction time. The time resolution of mass spectrometer is 40 s, fulfilling the detection of transient or stable species on a millisecond time scale. In addition, the reaction products are directly detected by mass spectrometer and different structural isomers can be distinguished by photoionization efficiency curves. The experiment utilizing Cl radical reaction with 1-butene and isobutene obtains the addition and abstraction products as well as their photoionization energies.

An Active Micromixer Based on Reverse Piezoelectricity Effect

The objective of this research effort was to design, fabricate, and characterize a high efficient active micromixer device with an integrated piezoelectric actuator to achieve rapid and homogeneous mixing inside a microfluidic channel. Efficient and rapid fluid mixing is an important task in microfluidic applications, such as chemical and biological analysis1, DNA hybridization, drug delivery2, and so on. Microfluidic devices are an excellent platform for carrying out chemical kinetic studies and nanomaterial research. However, due to the small size of microfluidic devises, fluid flow is constrained to the low Reynolds number regime, which indicates the absence of turbulence, and hence species mixing occurs primarily as a result of molecular diffusion which requires long mixing channels and extended retention times to achieve satisfactory mixing result3. Various micromixers have been developed in recent years4. They can be classified in two categories, passive and active. The passive micromixer usually requires long channel length in order to gain the long time needed for diffusion. However, as the driving force of fluid mixing in such devices is only molecular diffusion, it requires a long time to accomplish sufficient mixing. The active micromixers usually require more complicated structure and fabrication methods. However, due to short reaction time, high throughput, and reduced reagent consumption, and effectively mixing fluids make them attractive to many application5. In this study, we used a piezoelectric bimorph actuator (model no. T220-A4-503X. Piezo systems, INC.), which is composed of three layers (pzt-copper-pzt) and can provide very large reverse-piezoelectric deformation (on the order of micrometers). This deformation is directly used to induce fluid motion in the microchannel for mixing enhancement. To do so, the piezoelectric actuator was glued to the top wall of a shallow chamber, which is connected to the main mixing channel through a converging nozzle. The deformation of piezo (together with the soft top wall of the chamber) induces volume change of the chamber, which results in very strong in/out flow at the nozzle. This oscillatory in/out flow shows great promise in enhancing mixing in the channel.The preliminary results show that fluid mixing was remarkably promoted by the reverse piezoelectricity effect. Further optimization was deemed necessary to understand the effect of the reverse piezoelectricity, driving frequency, the driving voltage and the flow rates on mixing performance. Overall, our experiments demonstrate that reverse piezoelectricity effect facilitates simple and an inexpensive way to rapidly and homogenously mix fluid in a microchannel. References L. Wallman, E. Akesson, D. Ceric, P. Andersson, K. Day, O. Hovattta, S. Falci, T. Laurell, and E. Sundstrom, Lab Chip, 11, 3241 (2011)G. C. Prendergast, Nature, 478, 192 (2011)A. D. Stroock, S. K. W. Dertinger, A. Ajdari, I. Mezic, H. A. Stone, and G. M. Whitesides, Science, 295, 647 (2002)Y. K. Suh, S. Kang, Micromachines, 1, 82 (2010)K. S. Ryu, K. Shaikh, E. Goluch, Z. Fan and C. Liu, Lab Chip, 4, 608, (2004)P. H. Huang, Y. L. Xie, D. Ahmed, J. Rufo, N. Nama, Y. C. Chen, C. Y. Chan, and T. J. Huang, Lab on a Chip, 13, 3847 (2013)Y. L. Xie, D. Ahmed, M. I. Lapsley, S. S. Lin, A. A. Nawaz, L. Wang, and T. J. Huang, Analytical Chemistry, 84, 7495 (2012)Y. Xie, G. M. Whitesides, Annual Review of Materials Science, 28, 153 (1998)

A quantitative study of chemical kinetics for the synthesis of doped oxide nanocrystals using FTIR

The synthesis of Mg-doped ZnO nanocrystals was employed as a model system to quantitatively study the chemical kinetics of the precursor conversion reactions at synthetic conditions and the correlations with the formation of doped nanocrystals. An accurate method using Fourier transform infrared spectroscopy was developed to explore the alcoholysis reactions of the cationic precursors. Our study showed that three independent factors, molar ratio of dopant precursor, reaction temperature and coordination ligands of cationic precursors influenced the relative reactivity of magnesium to zinc precursor, and in turn the formation of Mg-doped ZnO nanocrystals with defined shapes and properties. This understanding underpins the advancement of the syntheses of doped nanocrystals and should be useful for future rational design of new synthetic systems.

HCl yield and chemical kinetics study of the reaction of Cl atoms with CH3I at the 298 K temperature using the infra-red tunable diode laser absorption spectroscopy

Pulsed ArF excimer laser (193nm) – CW infrared(IR) tunable diode laser Herriott type absorption spectroscopic technique has been made for the detection of product hydrochloric acid HCl. Absorption spectroscopic technique is used in the reaction chlorine atoms with methyl iodide (Cl+CH3I) to the study of kinetics on reaction Cl+CH3I and the yield of (HCl). The reaction of Cl+CH3I has been studied with the support of the reaction Cl+C4H10 (100% HCl) at temperature 298K. In the reaction Cl+CH3I, the total pressure of He between 20 and 125Torr at the constant concentration of [CH3I] 7.0×1014moleculecm−3. In the present work, we estimated adduct formation is very important in the reaction Cl+CH3I and reversible processes as well and CH3I molecule photo-dissociated in the methyl [CH3] radical. The secondary chemistry has been studied as CH3+CH3ICl=product, and CH3I+CH3ICl=product2. The system has been modeled theoretically for secondary chemistry in the present work. The calculated and experimentally HCl yield nearly 65% at the concentration 1.00×1014moleculecm−3 of [CH3I] and 24% at the concentration 4.0×1015moleculecm−3 of [CH3I], at constant concentration 4.85×1012moleculecm−3 of [CH3], and at 7.3×1012 moleculecm−3 of [Cl]. The pressure dependent also studied product of HCl at the constant [CH3], [Cl] and [CH3I]. The experimental results are also very good matching with the modelling work at the reaction CH3+CH3ICl=product (k=(2.75±0.35)×10−10s−1) and CH3I+CH3ICl=product2 (k=1.90±0.15)×10−12s−1. The rate coefficients of the reaction CH3+CH3ICl and CH3I+CH3ICl has been made in the present work. The experimental results has been studied by two method (1) phase locked and (2) burst mode.

The pyrolysis of 2-methylfuran: a quantum chemical, statistical rate theory and kinetic modelling study

Due to the rapidly growing interest in the use of biomass derived furanic compounds as potential platform chemicals and fossil fuel replacements, there is a simultaneous need to understand the pyrolysis and combustion properties of such molecules. To this end, the potential energy surfaces for the pyrolysis relevant reactions of the biofuel candidate 2-methylfuran have been characterized using quantum chemical methods (CBS-QB3, CBS-APNO and G3). Canonical transition state theory is employed to determine the high-pressure limiting kinetics, k(T), of elementary reactions. Rice-Ramsperger-Kassel-Marcus theory with an energy grained master equation is used to compute pressure-dependent rate constants, k(T,p), and product branching fractions for the multiple-well, multiple-channel reaction pathways which typify the pyrolysis reactions of the title species. The unimolecular decomposition of 2-methylfuran is shown to proceed via hydrogen atom transfer reactions through singlet carbene intermediates which readily undergo ring opening to form collisionally stabilised acyclic C5H6O isomers before further decomposition to C1-C4 species. Rate constants for abstraction by the hydrogen atom and methyl radical are reported, with abstraction from the alkyl side chain calculated to dominate. The fate of the primary abstraction product, 2-furanylmethyl radical, is shown to be thermal decomposition to the n-butadienyl radical and carbon monoxide through a series of ring opening and hydrogen atom transfer reactions. The dominant bimolecular products of hydrogen atom addition reactions are found to be furan and methyl radical, 1-butene-1-yl radical and carbon monoxide and vinyl ketene and methyl radical. A kinetic mechanism is assembled with computer simulations in good agreement with shock tube speciation profiles taken from the literature. The kinetic mechanism developed herein can be used in future chemical kinetic modelling studies on the pyrolysis and oxidation of 2-methylfuran, or the larger molecular structures for which it is a known pyrolysis/combustion intermediate (e.g. cellulose, coals, 2,5-dimethylfuran).

Effect of Change in Fuel Compositions and Heating Value on Ignition and Performance for Siemens SGT-400 Dry Low Emission Combustion System

The influence of changes in fuel composition and heating value on the performance of an industrial gas turbine combustor was investigated. The combustor tested was a single cannular combustor for Siemens SGT-400 13.4 MW dry low emission engine. Ignition, engine starting, emissions, combustion dynamics, and flash back through burner metal temperature monitoring were among the parameters investigated to evaluate the impact of fuel flexibility on combustor performance. Lean ignition and extinction limits were measured for three fuels with different heat values in term of Wobbe Index (WI): 25, 28.9, and 45 MJ/Sm3 (natural gas). The test results show that the air fuel ratio at lean ignition/extinction limits decreases and the margin between the two limits tends to be smaller as fuel heat value decreases. Engine start tests were also performed with a lower heating value fuel and results were found to be comparable to those for engine starting with natural gas. The combustor was further tested in a high pressure air facility at real engine operating conditions with different fuels covering WIs from 17.5 to 70 MJ/Sm3. The variation in fuel composition and heating value was achieved in a gas mixing plant by blending natural gas with CO2, CO, N2, and H2 (for the fuel with WI lower than natural gas) and C3H8 (for the fuel with WI higher than natural gas). Test results show that a benefit in NOx reduction can be seen for the lower WI fuels without H2 presence in the fuel and there are no adverse impacts on combustor performance except for the requirement of higher fuel supply pressure, however, this can be easily resolved by minor modification through the fuel injection design. Test results for the H2 enriched and higher WI fuels show that NOx, combustion dynamics and flash back have been adversely affected and major change in burner design is required. For the H2 enriched fuel, the effect of CO and H2 on combustor performance was also investigated for the fuels having a fixed WI of 29 MJ/Sm3. It is found that H2 dominates the adverse impact on combustor performance. The chemical kinetic study shows that H2 has significant effect on flame speed change and CO has significant effect on flame temperature change. Although the tests were performed on the Siemens SGT-400 combustion system, the results provide general guidance for the challenge of industrial gas turbine burner design for fuel flexibility.

Theoretical and Kinetic Study of the Hydrogen Atom Abstraction Reactions of Esters with HȮ2 Radicals

This work details an ab initio and chemical kinetic study of the hydrogen atom abstraction reactions by the hydroperoxyl radical (HȮ2) on the following esters: methyl ethanoate, methyl propanoate, methyl butanoate, methyl pentanoate, methyl isobutyrate, ethyl ethanoate, propyl ethanoate, and isopropyl ethanoate. Geometry optimizations and frequency calculations of all of the species involved, as well as the hindrance potential descriptions for reactants and transition states, have been performed with the Møller-Plesset (MP2) method using the 6-311G(d,p) basis set. A validation of all of the connections between transition states and local minima was performed by intrinsic reaction coordinate calculations. Electronic energies for all of the species are reported at the CCSD(T)/cc-pVTZ level of theory in kcal mol(-1) with the zero-point energy corrections. The CCSD(T)/CBS (extrapolated from CCSD(T)/cc-pVXZ, in which X = D, T, Q) was used for the reactions of methyl ethanoate + HȮ2 radicals as a benchmark in the electronic energy calculations. High-pressure limit rate constants, in the temperature range 500-2000 K, have been calculated for all of the reaction channels using conventional transition state theory with asymmetric Eckart tunneling corrections. The 1-D hindered rotor approximation has been used for the low frequency torsional modes in both reactants and transition states. The calculated individual and total rate constants are reported for all of the reaction channels in each reaction system. A branching ratio analysis for each reaction site has also been investigated for all of the esters studied in this work.