A detailed chemical kinetic mechanism has been developed to describe the oxidation of small hydrocarbon and oxygenated hydrocarbon species. The reactivity of these small fuels and intermediates is of critical importance in understanding and accurately describing the combustion characteristics, such as ignition delay time, flame speed, and emissions of practical fuels. The chosen rate expressions have been assembled through critical evaluation of the literature, with minimum optimization performed. The mechanism has been validated over a wide range of initial conditions and experimental devices, including flow reactor, shock tube, jet-stirred reactor, and flame studies. The current mechanism contains accurate kinetic descriptions for saturated and unsaturated hydrocarbons, namely methane, ethane, ethylene, and acetylene, and oxygenated species; formaldehyde, methanol, acetaldehyde, and ethanol.

A Hierarchical and Comparative Kinetic Modeling Study of C1 − C2 Hydrocarbon and Oxygenated Fuels

The fact that a new text book introducing the essentials of computational chemistry contains more than 500 pages shows impressively the grown and still growing size and importance of this field of chemistry. The author’s objectives of the book, using his own words, are “to provide a survey of computational chemistry its underpinnings, its jargon, its strengths and weaknesses that will be accessible to both the experimental and theoretical communities”. This design as a general introduction into computational chemistry makes it an alternative to Andrew R. Leach’s well-established “Molecular Modeling” (Prentice Hall) and Frank Jensen’s “Introduction to Computational Chemistry” (Wiley), although the latter focuses on the theory of electronic structure methods. Cramer’s “Essentials” covers force field and molecular orbital theory, Monte Carlo and Molecular Dynamics simulations, thermodynamic and electronic (spectroscopic) property calculation, condensed phase treatment and a few more topics. Moreover, the book contains thirteen selected case studies sexamples taken from the literature sto illustrate the application of the just presented theoretical and computational models. This especially makes the text book well suited for both classroom discussion and self-study. Each chapter of “Essentials” covers a main topic of computational chemistry and will be briefly described here; all chapters are ended by a bibliography and suggested additional readings as well as the literature references cited in the text. In chapter 1 the author defines basic terms such as “theory”, “model”, and “computation”, introduces the concept of the potential energy surface and provides some general considerations about hardware and software. Interestingly, the first equation occurring in the text is not Schro ̈dinger’s equation, as is the case for most computational chemistry introductions, but the famous Einstein relation. The second chapter deals with molecular mechanics. It explains the different potential energy contributions, introduces the field of structure optimization, and provides an overview of the variety of modern force fields. Chapter 3 covers the simulation of molecular ensembles. It defines phase space and trajectories and shows the formalism of, and problems and difference between, Monte Carlo and molecular dynamics. In chapter 4 the author introduces the foundations of molecular orbital theory. Basic concepts such as Hamilton operator, LCAO basis set approach, many-electron wave functions, etc. are explained. To illuminate the LCAO variational process, the Hu ̈ckel theory is presented with an example. Chapter 5 deals with semiempirical molecular orbital (MO) theory. Besides the classical approaches (extended Hu ̈ckel, CNDO, INDO, NDDO) and methods (e.g., MNDO, AM1, PM3) and their performance, examples are provided from the ongoing development in that still fascinating area. Ab initio MO theory is presented in chapter 6; the basis set concept is discussed in detail, and, after some considerations from an user’s point of view, the general performance of ab initio methods is explicated. The next chapter covers the problem of electron correlation and gives the most prominent solutions for its treatment: configuration interaction, theory of the multiconfiguration self-consistent field, perturbation, and coupled cluster. Practical issues are also discussed. Chapter 8’s topic is density functional theory (DFT). Its theoretical foundation, methodology, and some functionals as well as its pros and cons compared to MO theory are presented together with a general performance overview. The next two chapters deal with charge distribution, derived and spectroscopic properties (e.g., atomic charges, polarizability, rotational, vibrational, and NMR spectra), and thermodynamic properties (e.g., zero-point vibrational energy, free energy of formation, and reaction). The modeling of condensed phases is addressed in chapters 11 (implicit models) and 12 (explicit models), which closes with a comparison between the two approaches. Chapter 13 familiarizes the reader with hybrid quantum mechanical/molecular mechanical (QM/MM) models. Polarization as well as the problematic implications of unsaturated QM and MM components are discussed, and empirical valence bond methods are also presented. The treatment of excited states is the topic of chapter 14; besides CI and MCSCF as computational methods, transition probabilities and solvatochromism are discussed. The last chapter deals with reaction dynamics, mostly adiabaticskinetics, rate constants, reaction paths, and transition state theory are section topics here sbut also nonadiabatic, introducing curve crossing and Marcus theory in brief. The appendix is divided into four parts: an acronym glossary (which is very helpful), an overview of symmetry and group theory, an introduction to spin algebra, and finally a section about orbital localization. A rather detailed index ends the book. The “Essentials” writing style fits the fascinating topic: one reads on and on andssurprise! sanother chapter has been absorbed. The text is complemented by a large number of black and white figures and clear tables, mostly self-explanatory with descriptive captions. The use of equations and mathematical formulas in general is well-balanced, and the level of math should be understandable for every natural scientist with some basic knowledge of physics. There are only a few minor shortcomings: for example, a literature reference cited in the text (“Beck et al.”, p 142) is missing in the bibliography; “Kronecker” is mistyped with o ̈; and the author completely forgot to reference Leach’s text book when referring to other computational chemistry introductions. However, the author has established a specific errata web page (http://pollux.chem.umn.edu/ ∼cramer/Errors.html) with all known errors. These will be corrected in the next printing or next revised edition, respectively. With its emphasis, on one hand, on the basic concepts and applications rather than pure theory and mathematics, and on the other hand, coverage of quantum mechanical and classical mechanical models including examples from inorganic, organic, and biological chemistry, “Essentials” is a useful tool not only for teaching and learning but also as a quick reference, and thus will most probably become one of the standard text books for computational chemistry.

Essentials Of Computational Chemistry Theories And Models

A detailed chemical kinetic model for ethanol oxidation has been developed and validated against a variety of experimental data sets. Laminar flame speed data (obtained from a constant volume bomb and counterflow twin-flame), ignition delay data behind a reflected shock wave, and ethanol oxidation product profiles from a jet-stirred and turbulent flow reactor were used in this computational study. Good agreement was found in modeling of the data sets obtained from the five different experimental systems. The computational results show that high temperature ethanol oxidation exhibits strong sensitivity to the fall-off kinetics of ethanol decomposition, branching ratio selection for C2H5OH + OH Products, and reactions involving the hydroperoxyl (HO2) radical.



The multichanneled ethanol decomposition process is analyzed by RRKM/Master Equation theory, and the results are compared with those obtained from earlier studies. The ten-parameter Troe form is used to define the C2H5OH(+M) CH3 + CH2OH(+M) rate expression as 


k∞ = 5.94E23 T−1.68 exp(−45880 K/T) (s−1)




ko = 2.88E85 T−18.9 exp(−55317 K/T) (cm3/mol/sec)




Fcent = 0.5 exp(−T/200 K) + 0.5 exp(−T/890 K) + exp(−4600 K/T)



and the C2H5OH(+M) C2H4 + H2O(+M) rate expression as 


k∞ = 2.79E13 T0.09 exp(−33284 K/T) (s−1)




ko = 2.57E83 T−18.85 exp(−43509 K/T) (cm3/mol/sec)




F cent = 0.3 exp(−T/350 K) + 0.7 exp(−T/800 K) + exp(−3800 K/T)



with an applied energy transfer per collision value of = 500 cm−1.



An empirical branching ratio estimation procedure is presented which determines the temperature dependent branching ratios of the three distinct sites of hydrogen abstraction from ethanol. The calculated branching ratios for C2H5OH + OH, C2H5OH + O, C2H5OH + H, and C2H5OH + CH3 are compared to experimental data. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 183–220, 1999

A detailed chemical kinetic model for high temperature ethanol oxidation

Alcohol combustion chemistry

Hot compressed water (HCW, here water above 200 °C) possesses very interesting properties This series of articles gives an overview of the state of the art as regards the understanding of reactions in HCW In the first part the macroscopic and microscopic properties of HCW will be described, followed by a summary of synthesis reactions published The impact of the unique properties shall be discussed in part II, with the thermal degradation of tert-butylbenzene and the oxidation of methanol being used as examples The studies reported will show that the microscopic properties are of more importance to understanding reactions in HCW than assumed in the past

Hot compressed water as reaction medium and reactant properties and synthesis reactions

Experimental data on the enthalpies of formation of chloromethanes, chloroethynes, chloroethenes, and chloroethanes are critically reviewed. Enthalpy of formation values for the C1 and C2 chlorinated hydrocarbons are highly cross-linked by various measured reaction equilibria and currently available sets of values are not internally self-consistent. It is shown that the early static bomb combustion calorimetry studies on highly chlorinated compounds generally give enthalpies of formation that are systematically more positive than later values derivable from rotating bomb combustion or equilibria studies. Those previously recommended values which were based mainly on the early static bomb work therefore need substantial revision. On the basis of more recent literature data obtained with rotating bomb combustion calorimetry, together with analyses of literature data on other reaction enthalpies and equilibria involving chlorinated hydrocarbons, an updated self-consistent set of ΔfHo[298.15 K] values for clo...

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Evaluated Enthalpies of Formation of the Stable Closed Shell C1 and C2 Chlorinated Hydrocarbons

Rates, products, and mechanisms in the gas-phase hydrogenolysis of phenol between 922 and 1175 K

Normal hexyl radicals generated from the decomposition of n-hexyl iodide have been decomposed in single pulse shock tube experiments. All the products arising from the decomposition of 1-hexyl (the initial reactant) and 2-hexyl and 3-hexyl (isomerization products) have been detected in the temperature range 890–1020 K and 1.5–5 bar pressures. We find that k ( C 6 H 13 - 3 = > C 2 H 5 + 1 - C 4 H 8 ) / k ( C 6 H 13 - 3 = > CH 3 + 1 - C 5 H 10 ) = 3.4 ± 0.1 when this is combined with literature values of the beta bond scission reactions of hexyl radicals we find the following high pressure rate expressions for the isomerization processes; k ( C 6 H 13 - 1 = > C 6 H 13 - 2 ) = 1.83 × 10 2 T 2.55 exp ( - 5516 / T ) s - 1 k ( C 6 H 13 - 1 = > C 6 H 13 - 3 ) = 6.98 × T 3.2 exp ( - 8333 / T ) s - 1 with an uncertainty of a factor of 1.5 in the rate constants and 5 kJ/mol in the activation energy. They are compatible with low as well as the high temperature results. The effects of energy transfer have been deduced from a master equation RRKM analysis covering the pressure range of 0.1–100 bar, 500–1900 K. The low reaction thresholds and multichannel nature of the process leads to special problems. These include a non-monotonic decrease in rate constants from high pressure values with increasing temperature and rate constants in the “fall-off” region that are dependent on the initial isomer. Overall effects are minimal in the 100 bar region. Maximum deviation from high pressure behavior is approximately an order of magnitude near 1000 K for reactions in the 1 bar region.

The decomposition of normal hexyl radicals

The thermal cracking patterns from the decomposition and isomerization of octyl-1 radicals have been determined from the pyrolysis of n -octyl iodide in single pulse shock tube experiments at temperatures in the 850–1000 K range and pressures near 2 bar. Rate constants for the six beta bond scission and five of the six isomerization processes have been derived over all combustion conditions [0.1–100 bar, 700–1900 K]. Comparisons are made with previous studies on the decomposition of other primary radicals. Results are consistent with similar types of reactions having equal rate constants. The larger size of the octyl radicals makes contributions from secondary to secondary radical isomerization increasingly important. The results confirm that the 1–3 H-transfer process (involving a seven member cyclic transition state) have rate constants that are within a factor of 2 of those for the 1–4 process (six member cyclic transition state) It appears that rate constants for 1–2 H-transfer isomerization, involving an eight member cyclic transition state is unimportant in comparison to contributions from other isomerization processes. The strain energy does not appear to play an important role for these larger transition states. The implications of these results to larger fuel radicals will be discussed.

Multichannel decomposition and isomerization of octyl radicals

Tetraethoxysilane (TEOS) has been decomposed in single-pulse shock tube experiments over the temperature range 1160−1285 K and pressures of about 150 kPa (1.5 bar). The main observed products are ethylene and ethanol. The yields of these products as a percentage of decomposed TEOS increase with temperature. Studies have also been carried out with tetra-n-propoxysilane (TPOS), dimethyldiethoxysilane (DMDEOS), and trimethylethoxysilane (TMEOS). Evidence is presented that in all cases the main initial reaction is a 1,2-elimination to form the olefin and the corresponding silanol. A smaller contribution from C−C bond-breaking channels is also observed. In combination with lower temperature results and the thermochemistry, the following rate expressions for the elementary processes are recommended:  k[TEOS → C2H4 + HOSi(OC2H5)3] = 1.04 × 1010T1.1 exp(−30 950 K/T) s-1; k[TEOS → CH3 + CH2OSi(OC2H5)3] = 4 × 1017 exp(−43 300 K/T) s-1. The observed ethanol product is postulated to arise from decomposition of the si...

Jeffrey A. Manion

Papers

Evaluated Enthalpies of Formation of the Stable Closed Shell C1 and C2 Chlorinated Hydrocarbons

Rates, products, and mechanisms in the gas-phase hydrogenolysis of phenol between 922 and 1175 K

The decomposition of normal hexyl radicals

Multichannel decomposition and isomerization of octyl radicals

Single-Pulse Shock Tube Study of the Decomposition of Tetraethoxysilane and Related Compounds