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We have discovered a new and highly competitive product channel in the unimolecular decay process for small Criegee intermediates, CH2OO and anti/syn-CH3C(H)OO, occurring by intramolecular insertion reactions via a roaming-like transition state (TS) based on quantum-chemical calculations. Our results show that in the decomposition of CH2OO and anti-CH3C(H)OO, the predominant paths directly produce cis-HC(O)OH and syn-CH3C(O)OH acids with >110 kcal/mol exothermicities via loose roaming-like insertion TSs involving the terminal O atom and the neighboring C-H bonds. For syn-CH3C(H)OO, the major decomposition channel occurs by abstraction of a H atom from the CH3 group by the terminal O atom producing CH2C(H)O-OH. At 298 K, the intramolecular insertion process in CH2OO was found to be 600 times faster than the commonly assumed ring-closing reaction. [ABSTRACT FROM AUTHOR]

We investigated the reaction dynamics of O(¹D) towards hydrogen atoms of two types in HCOOH. The reaction was initiated on irradiation of a flowing mixture of O3 and HCOOD or DCOOH at 248 nm. The relative vibration-rotational populations of OH and OD (1 ≦ v ≦ 4, J ≤ 15) states were determined from time-resolved IR emission recorded with a step-scan Fourier-transform spectrom-eter. In the reaction of O(¹D) + HCOOD, the rotational distribution of product OH is nearly Boltz-mann, whereas that of OD is bimodal. The product ratio [OH]/[OD] is 0.16 ± 0.05. In the reaction of O(¹D) + DCOOH, the rotational distribution of product OH is bimodal, but the observed OD lines are too weak to provide reliable intensities. The three observed OH/OD channels agree with three major channels of production predicted with quantum-chemical calculations. In the case of O(¹D) + HCOOD, two intermediates HOC(O)OD and HC(O)OOD are produced in the initial C-H and O-D insertion, respectively. The former undergoes further decomposition of the newly formed OH or the original OD, whereas the latter produces OD via direct decomposition. Decomposition of HOC(O)OD produced OH and OD with similar vibrational excitation, indicating efficient in-tramolecular vibrational relaxation, IVR. Decomposition of HC(O)OOD produced OD with greater rotational excitation. The predicted [OH]/[OD] ratio is 0.20 for O(¹D) + HCOOD and 4.08 for O(¹D) + DCOOH; the former agrees satisfactorily with experiments. We also observed the v3 emission from the product CO2. This emission band is deconvoluted into two components corresponding to internal energies E = 317 and 96 kJ mol-1 of CO2, predicted to be produced via direct dehydration of HOC(O)OH and secondary decomposition of HC(O)O that was produced via decomposition of HC(O)OOH, respectively. [ABSTRACT FROM AUTHOR]

This paper reports the first quantitative ab initio prediction of the disproportionation/combination ratio of alkyl+alkyl reactions using CH[sub 3]+C[sub 2]H[sub 5] as an example. The reaction has been investigated by the modified Gaussian-2 method with variational transition state or Rice–Ramsperger–Kassel–Marcus calculations for several channels producing (1) CH[sub 4]+CH[sub 2]CH[sub 2], (2) C[sub 3]H[sub 8], (3) CH[sub 4]+CH[sub 3]CH, (4) H[sub 2]+CH[sub 3]CHCH[sub 2], (5) H[sub 2]+CH[sub 3]CCH[sub 3], and (6) C[sub 2]H[sub 6]+CH[sub 2] by H-abstraction and association/decomposition mechanisms through singlet and triplet potential energy paths. Significantly, the disproportionation reaction (1) producing CH[sub 4]+C[sub 2]H[sub 4] was found to occur primarily by the lowest energy path via a loose hydrogen-bonding singlet molecular complex, H[sub 3]C··HC[sub 2]H[sub 4], with a 3.5 kcal/mol binding energy and a small decomposition barrier (1.9 kcal/mol), instead of a direct H-abstraction process. Bimolecular reaction rate constants for the formation of the above products have been calculated in the temperature range 300–3000 K. At 1 atm, formation of C[sub 3]H[sub 8] is dominant below 1200 K. Over 1200 K, the disproportionation reaction becomes competitive. The sum of products (3)–(6) accounts for less than 0.3% below 1500 K and it reaches around 1%–4% above 2000 K. The predicted rate constant for the disproportionation reaction with multiple reflections above the complex well, k[sub 1]=5.04×T[sup 0.41] exp(429/T) at 200–600 K and k[sub 1]=1.96×10[sup -20] T[sup 2.45] exp(1470/T) cm[sup 3] molecule[sup -1] s[sup -1] at 600–3000 K, agrees closely with experimental values. Similarly, the predicted high-pressure rate constants for the combination reaction forming C[sub 3]H[sub 8] and its reverse dissociation reaction in the temperature range 300–3000 K, k[sub 2][sup ∞]=2.41×10[sup -10] T[sup -0.34] exp(259/T) cm[sup 3] molecule[sup -1] s[sup -1] and k[sub -2][sup ∞]=8.89×10[sup 22] T[sup -1.67]exp(-46 037/T) s[sup -1], respectively, are also in good agreement with available experimental data. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The mechanism for the CH[sub 3]+C[sub 2]H[sub 5]OH reaction has been investigated by the modified Gaussian-2 method based on the geometric parameters of the stationary points optimized at the B3LYP/6-311+G(d,p) level of theory. Five transition states have been identified for the production of CH[sub 4]+CH[sub 3]CHOH (TS1), CH[sub 4]+CH[sub 3]CH[sub 2]O (TS2), CH[sub 4]+CH[sub 2]CH[sub 2]OH (TS3), CH[sub 3]OH+CH[sub 3]CH[sub 2] (TS4), and CH[sub 3]CH[sub 2]OCH[sub 3]+H (TS5) with the corresponding barriers 12.0, 13.2, 16.0, 44.7, and 49.9 kcal/mol, respectively. The predicted rate constants and branching ratios for the three lower-energy H-abstraction reactions were calculated using the conventional and variational transition state theory with quantum-mechanical tunneling corrections for the temperature range 300–3000 K. The predicted total rate constant, k[sub t]=8.36×10[sup -76] T[sup 20.00] exp(5258/T) cm[sup 3] mol[sup -1] s[sup -1] (300–600 K) and 6.10×10[sup -25] T[sup 4.10]exp(-4058/T) cm[sup 3] mol[sup -1] s[sup -1] (600–3000 K), agrees closely with existing experimental data in the temperature range 403–523 K. Similarly, the predicted rate constants for CH[sub 3]+CH[sub 3]CD[sub 2]OH and CD[sub 3]+C[sub 2]H[sub 5]OD are also in reasonable agreement with available low temperature kinetic data. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The isomerization and decomposition of ClOO and OClO radicals and related Cl + O[sub 2] and O + ClO reactions have been investigated by ab initio molecular orbital and transition-state theory calculations. The species involved have been optimized at the PW91PW91/6-311+G(3df) level and their energies refined by single-point calculations with the modified Gaussian-2 method. Predicted bond-dissociation energies of ClOO and OClO, D[sub 0](Cl-OO) = 4.6 and D[sub 0](O-ClO) = 58.5 kcal/mol, agree well with experimental values. Calculated rate constants for the Cl + O[sub 2] → ClOO reaction in 160-1000 K at the high- and low-pressure limits can be expressed by k[sub 1, sup ∞] = 1.8 ± 0.1 × 10[sup -10] cm³ molecule[sup -1] s[sup -1] and k[sub 1](He) = 1.66 × 10[sup -19] T[sup -5.34] exp(-675/T) and k[sub 1, sup 0](O[sub 2]) = 1.26 × 10[sup -16] T[sup -6.22] exp(-943/T) cm[sup 6] molecule[sup -2] s[sup -1]. For Ar and N[sub 2], theory underpredicts k[sub 1, sup 0](M) below room temperature due to significant contributions from the "chaperon" mechanism involving Cl-M complexes. The corresponding rate constants for O + ClO→OClO are predicted to be: k[sub 2, sup ∞] = 4.33 × 10[sup -11] T[sup -0.03] exp(43/T) cm³ molecule[sup -1] s[sup -1] and k[sub 2, sup 0] = 8.60 × 10[sup -21] T[sup -4.1] exp(-420/T) cm[sup 6] molecule[sup -2] s[sup -1] for 200-1000 K with N[sub 2] as the third body. The O + ClO reaction producing Cl + O[sub 2] via ClOO was found to be pressure-independent with k[sub 3] = 4.11 × 10[sup -11] T[sup -0.06] exp(42/T) cm³ molecule[sup -1] s[sup -1]. For the dissociation of ClOO, the rate constants are predicted to be: k[sub -1, sup ∞] = 6.17 × 10[sup 15] T[sup -0.46] 1.89 × 10[sup 7] exp(-2570/T) s[sup -1] and k[sub -1, sup 0] = T[sup -5.88] × exp(-3280/T) cm³ molecule[sup -1] s[sup -1] for 160-500 K with O[sub 2] as the third-body. The corresponding... [ABSTRACT FROM AUTHOR]

The kinetics and mechanism for the H + C[SUB2]H[SUB5]OH reaction, a key chain-propagation step in the high temperature decomposition and combustion of ethanol, have been investigated with the modified GAUSSIAN -2 (G2M) method using the structures of the reactants, transition states and products optimized at the B3LYP/6-311 + G(d,p) level of theory. Four transition states have been identified for the production of H[SUB2] + CH[SUB3](CHOH)(TS1), H[SUB2] + CH[SUB2]C[SUB2]OH (TS2), H[SUB2] + C[SUB2]H[SUB5]O (TS3), and H[SUB2]O + C[SUB2]H[SUB5] (TS4) with the corresponding barriers, 7.18, 13.30, 14.95, and 27.10 kcal/mol. The predicted rate constants and branching ratios for the three H-abstraction reactions have been calculated over the temperature range 300-3000 K using the conventional and variational transition state theory with quantum-mechanical tunneling corrections. The predicted total rate constant, k[SUBt] = 3.15 × 10[SUP3]T[SUP3.12] exp(-1508/T) cm[SUP3] mol[SUP-1]s[SUP-1], agrees reasonably with existing experimental data; in particular, the result at 423 K was found to agree quantitatively with an available experimental value. The small deviation between the predicted k[SUBt] and another set of experimental data measured at 295-700 K has been examined by kinetic modeling; the deviation is attributable to insufficient corrections for contributions from secondary reactions. [ABSTRACT FROM AUTHOR]

The unimolecular decomposition of iso-C[sub 3]H[sub 7]OH has been studied with a modified GAUSSIAN-2 method. Among the six low-lying product channels identified, the H[sub 2]O-elimination process (2) via a four-member-ring transition state is dominant below 760 Torr over the temperature range 500-2500 K. At higher pressures and over 1200 K, the cleavage of a C-C bond by reaction (1) producing CH[sub 3]+CH[sub 3]C(H)OH is predicted to be dominant. The predicted low- and high-pressure limit rate constants for these two major product channels can be given by k[sup 0, sub 1] = 6.3 × 10[sup 42] T[sup -16.21] exp(-47 400/T), k[sup 0, sub 2] = 7.2 × 10[sup 44] T[sup -14.70] exp(--35 700/T) cm³ molecule[sup -1] s[sup -1], k[sup ∞, sub 1] = 8.0 × 10[sup 29] T[sup -3.75] exp(-45 800/T), and k[sup ∞, sub 2] = 2.0 × 10[sup 6] T[sup 2.12] exp(-30 700/T) s[sup -1], respectively. Predicted k[sup l] values compare reasonably with available experimental data; however, k[sub 2] values are lower than the experimentally determined apparent rate constant for C[sub 3]H[sub 6] formation, which may derive in large part from secondary radical reactions. Other minor decomposition products were predicted to have the barriers H[sub 2]+CH[sub 3]C(O)CH[sub 3], E[sup 0, sub 3]=82.8kcal/mol; H[sub 2]O+¹CH[sub 3]CCH[sub 3], E[sup 0, sub 4] = 77.9 kcal/mol; CH[sub 4] + CH[sub 3] C(H)O, E[sup 0, sub 5] = 84.3 kcal/mol; and CH[sub 4] + ¹CH[sub 3] COH, E[sup 0, sub 6] = 81.9 kcal/ mol. The triplet-singlet energy gap for CH[sub 3]CCH[sub 3] was predicted to be 5.2 kcal/mol, favoring the singlet state. [ABSTRACT FROM AUTHOR]

The unimolecular decomposition of CH[sub 3]CH[sub 2]OH has been investigated at the G2M (RCC2) level of theory. The decomposition reaction was found to be dependent strongly on pressure and temperature. Among the eight product channels identified, the H[sub 2]O-elimination process (1) via a four-member-ring transition state is dominant below 10 atm in the temperature range of 700-2500 K. At the high—pressure limit and over 1500 K, cleavage of the C-C bond by reaction (2) producing CH[sub 3] + CH[sub 2]OH is predicted to be dominant while the CH[sub 3]CH[sub 2]+OH channel (8) also becomes competitive. The predicted high-pressure rate constants for the two major product channels can be given by k[sub l] =7.0 × 10[sup 13] exp(-34200/T) and k[sub 2]=3.7 × 10[sup 26] T[sup -2.95] exp(-45 600/T) s[sup -1], which compare reasonably with earlier data and with our preliminary experimental result obtained in a shock tube and static cell study. At the internal energy corresponding to the O(¹D)+C[sub 2]H[sub 6] reaction (140.7 kcal/mol above C[sub 2]H[sub 5]OH), the predicted branching ratios for the production of CH[sub 3], C[sub 2]H[sub 5], and H[sub 2] are in qualitative agreement with the result of a recent cross-molecular beam experiment. [ABSTRACT FROM AUTHOR]

Criegee intermediates, which are carbonyl oxides produced when ozone reacts with unsaturated hydrocarbons, play an important role in the formation of OH and organic acids in the atmosphere, but they have eluded direct detection until recently. Reactions that involve Criegee intermediates are not understood fully because data based on their direct observation are limited. We used transient infrared absorption spectroscopy to probe directly the decay kinetics of formaldehyde oxide (CH2OO) and found that it reacts with itself extremely rapidly. This fast self-reaction is a result of its zwitterionic character. According to our quantum-chemical calculations, a cyclic dimeric intermediate that has the terminal O atom of one CH2OO bonded to the C atom of the other CH2OO is formed with large exothermicity before further decomposition to 2H2CO + O2(1Δg). We suggest that the inclusion of this previously overlooked rapid reaction in models may affect the interpretation of previous laboratory experiments that involve Criegee intermediates. [ABSTRACT FROM AUTHOR]

Telomere maintenance is essential for cancer growth. Induction of telomere dysfunction, for example, by inhibition of telomeric proteins or telomerase, has been shown to strongly enhance cancer cells' sensitivity to chemotherapies. However, it is not clear whether modulations of telomere maintenance constitute cancer cellular responses to chemotherapies. Furthermore, the manner in which anti-cancer drugs affect telomere function remains unknown. In this study, we show that anthracyclines, a class of anti-cancer drugs widely used in clinical cancer treatments, have an active role in triggering telomere dysfunction specifically in telomerase-positive cancer cells. Anthracyclines interrupt telomere maintenance by telomerase through the downregulation of PinX1, a protein factor responsible for targeting telomerase onto telomeres, thereby inhibiting telomerase association with telomeres. We further demonstrate that anthracyclines downregulate PinX1 by inducing this protein degradation through the ubiquitin-proteasome-dependent pathway. Our data not only reveal a novel action for anthracyclines as telomerase functional inhibitors but also provide a clue for the development of novel anti-cancer drugs based on telomerase/telomere targeting, which is actively investigated by many current studies. [ABSTRACT FROM AUTHOR]

The mechanisms for reactions of H, HO, and Cl with HOClO3, important elementary processes in the early stages of the ammonium perchlorate (AP) combustion reaction, have been investigated at the CCSD(T)/6-311+G(3df,2p)//PW91PW91/6-311+G(3df) level of theory. The rate constants for the low-energy channels have been calculated by statistical theory. For the reaction of H and HOClO3, the main channels are the production of H2 + ClO4 (k1a) and HO + HOClO2 (k1b); k1a and k1b can be represented as 1.07 × 10-17 T1.97 exp(-7484/T) and 6.08 × 10-17T1.96 exp(-7729/T) cm3 molecule-1 s-1, respectively. For the HO + HOClO3 reaction, the main pathway is the H2O + ClO4 (k2a) production process, with the predicted rate constant k2a = 1.24 × 10 -8 T-2.99 exp(1664/T) for 300–500 K and k2a = 1.27×10-19 T2.12 exp(-1474/T) for 500–3000 K. For the Cl + HOClO3 reaction, the formation of HOCl + ClO3 (k3a) and HCl + ClO4 (k3b) is dominant, with k3a = 1.33×10-12 T0.67 exp(-9658/T) and k3b = 1.75×1016 T1.63 exp(-11156/T) cm3 molecules-1 in the range of 300–3000 K. In addition, the heats of formation of ClO3 and HOClO3 have been predicted based on several isodesmic and/or isogyric reactions with ΔfHo0 (ClO3) = 47.0 ± 1.0 and ΔfHo0 (HOClO3) = 5.5 ± 1.5 kcal/mol, respectively. These data may be used for kinetic simulation of the AP decomposition and combustion reaction. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 253–261, 2010 [ABSTRACT FROM AUTHOR]

The mechanisms for reactions of H, HO, and Cl with HOClO3, important elementary processes in the early stages of the ammonium perchlorate (AP) combustion reaction, have been investigated at the CCSD(T)/6-311+G(3df,2p)//PW91PW91/6-311+G(3df) level of theory. The rate constants for the low-energy channels have been calculated by statistical theory. For the reaction of H and HOClO3, the main channels are the production of H2 + ClO4 (k1a) and HO + HOClO2 (k1b); k1a and k1b can be represented as 1.07 × 10-17 T1.97 exp(-7484/T) and 6.08 × 10-17T1.96 exp(-7729/T) cm3 molecule-1 s-1, respectively. For the HO + HOClO3 reaction, the main pathway is the H2O + ClO4 (k2a) production process, with the predicted rate constant k2a = 1.24 × 10 -8 T-2.99 exp(1664/T) for 300–500 K and k2a = 1.27×10-19 T2.12 exp(-1474/T) for 500–3000 K. For the Cl + HOClO3 reaction, the formation of HOCl + ClO3 (k3a) and HCl + ClO4 (k3b) is dominant, with k3a = 1.33×10-12 T0.67 exp(-9658/T) and k3b = 1.75×1016 T1.63 exp(-11156/T) cm3 molecules-1 in the range of 300–3000 K. In addition, the heats of formation of ClO3 and HOClO3 have been predicted based on several isodesmic and/or isogyric reactions with ΔfHo0 (ClO3) = 47.0 ± 1.0 and ΔfHo0 (HOClO3) = 5.5 ± 1.5 kcal/mol, respectively. These data may be used for kinetic simulation of the AP decomposition and combustion reaction. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 253–261, 2010 [ABSTRACT FROM AUTHOR]

The kinetics and mechanism for the thermal decomposition of diketene have been studied in the temperature range 510–603 K using highly diluted mixtures with Ar as a diluent. The concentrations of diketene, ketene, and CO2 were measured by FTIR spectrometry using calibrated standard mixtures. Two reaction channels were identified. The rate constants for the formation of ketene (k1) and CO2 (k2) have been determined and compared with the values predicted by the Rice–Ramsperger–Kassel–Marcus (RRKM) theory for the branching reaction. The first-order rate constants, k1 (s-1) = 1015.74 ± 0.72 exp(-49.29 (kcal mol-1) (±1.84)/RT) and k2 (s-1) = 1014.65 ± 0.87 exp(-49.01 (kcal mol-1) (±2.22)/RT); the bulk of experimental data agree well with predicted results. The heats of formation of ketene, diketene, cyclobuta-1,3-dione, and cyclobuta-1,2-dione at 298 K computed from the G2M scheme are -11.1, -45.3, -43.6, and -40.3 kcal mol-1, respectively. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 580–590, 2007 [ABSTRACT FROM AUTHOR]

We investigated the reactivity of O(1D) towards two types of hydrogen atoms in CH3OH. The reaction was initiated on irradiation of a flowing mixture of O3 and CD3OH or CH3OD at 248 nm. Relative vibration-rotational populations of OH and OD (1 ≤ v ≤ 4) states were determined from their infrared emission recorded with a step-scan time-resolved Fourier-transform spectrometer. In O(1D) + CD3OH, the rotational distribution of OD is nearly Boltzmann, whereas that of OH is bimodal; the product ratio [OH]/[OD] is 1.56 ± 0.36. In O(1D) + CH3OD, the rotational distribution of OH is nearly Boltzmann, whereas that of OD is bimodal; the product ratio [OH]/[OD] is 0.59 ± 0.14. Quantum-chemical calculations of the potential energy and microcanonical rate coefficients of various channels indicate that the abstraction channels are unimportant and O(1D) inserts into the C-H and O-H bonds of CH3OH to form HOCH2OH and CH3OOH, respectively. The observed three channels of OH are consistent with those produced via decomposition of the newly formed OH or the original OH moiety in HOCH2OH or decomposition of CH3OOH. The former decomposition channel of HOCH2OH produces vibrationally more excited OH because of incomplete intramolecular vibrational relaxation, and decomposition of CH3COOH produces OH with greater rotational excitation, likely due to a large torque angle during dissociation. The predicted [OH]/[OD] ratios are 1.31 and 0.61 for O(1D) + CD3OH and CH3OD, respectively, at collision energy of 26 kJ mol-1, in satisfactory agreement with the experimental results. These predicted product ratios vary weakly with collision energy. [ABSTRACT FROM AUTHOR]

The kinetics and mechanism for the reaction of ClOO with NO have been investigated by ab initio molecular orbital theory calculations based on the CCSD(T)/6-311+G(3df)//PW91PW91/6-311+G(3df) method, employed to evaluate the energetics for the construction of potential energy surfaces and prediction of reaction rate constants. The results show that the reaction can produce two key low energy products ClNO + 3O2 via the direct triplet abstraction path and ClO + NO2 via the association and decomposition mechanism through long-lived singlet pc-ClOONO and ClONO2 intermediates. The yield of ClNO + O2 (1▵) from any of the singlet intermediates was found to be negligible because of their high barriers and tight transition states. As both key reactions initially occur barrierlessly, their rate constants were evaluated with a canonical variational approach in our transition state theory and Rice-Ramspergen-Kassel-Marcus/master equation calculations. The rate constants for ClNO + 3O2 and ClO + NO2 production from ClOO + NO can be given by 2.66 × 10-16 T1.91 exp(341/T) (200-700 K) and 1.48 × 10-24 T3.99 exp(1711/T) (200-600 K), respectively, independent of pressure below atmospheric pressure. The predicted total rate constant and the yields of ClNO and NO2 in the temperature range of 200-700 K at 10-760 Torr pressure are in close agreement with available experimental results. [ABSTRACT FROM AUTHOR]

Thekinetics and mechanism of the CH3+ O reaction andrelated isomerization–decomposition of CH3O andCH2OH radicals have been studied by ab initio molecularorbital theory based on the CCSD(T)/aug-cc-pVTZ//CCSD/aug-cc-pVTZ,CCSD/aug-cc-pVDZ, and G2M//B3LYP/6-311+G(3df,2p) levels of theory.The predicted potential energy surface of the CH3+ O reactionshows that the CHO + H2products can be directly generatedfrom CH3O by the TS3 → LM1 → TS7 →LM2 → TS4 path, in which both LM1 and LM2 are very loose andTS7 is roaming-like. The result for the CH2O + H reactionshows that there are three low-energy barrier processes includingCH2O + H → CHO + H2via H-abstractionand CH2O + H → CH2OH and CH2O + H → CH3O by addition reactions. The predictedenthalpies of formation of the CH2OH and CH3O radicals at 0 K are in good agreement with available experimentaldata. Furthermore, the rate constants for the forward and some keyreverse reactions have been predicted at 200–3000 K under variouspressures. Based on the new reaction pathway for CH3+O, the rate constants for the CH2O + H and CHO + H2reactions were predicted with the microcanonical variationaltransition-state/Rice–Ramsperger–Kassel–Marcus(VTST/RRKM) theory. The predicted total and individual product branchingratios (i.e., CO versus CH2O) are in good agreement withexperimental data. The rate constant for the hydrogen abstractionreaction of CH2O + H has been calculated by the canonicalvariational transition-state theory with quantum tunneling and small-curvaturecorrections to be k(CH2O + H →CHO + H2) = 2.28 × 10–19T2.65exp(−766.5/T) cm3molecule–1s–1for the 200–3000 K temperaturerange. The rate constants for the addition giving CH3Oand CH2OH and the decomposition of the two radicals havebeen calculated by the microcanonical RRKM theory with the time-dependentmaster equation solution of the multiple quantum well system in the200–3000 K temperature range at 1 Torr to 100 atm. The predictedrate constants are in good agreement with most of the available data. [ABSTRACT FROM AUTHOR]

Thekinetics for the thermal unimolecular decomposition of CH3NO2and its structural isomer CH3ONOhave been investigated by statistical theory calculations based onthe potential energy surface calculated at the UCCSD(T)/CBS and CASPT3(8,8)/6-311+G(3df,2p) levels. Our results show that for the decompositionof CH3NO2at pressures less than 2 Torr, isomerizationto CH3ONO via the recently located roaming transition stateis dominant in the entire temperature range studied, 400–3000K. However, at higher pressures, the formation of the commonly assumedproducts, CH3+ NO2, becomes competitive andat pressures higher than 200 Torr the production of CH3+ NO2is exclusive. The predicted rate constants for760 Torr and the high-pressure limit with Ar as diluent in the temperaturerange 500–3000 K, producing solely CH3+ NO2, can be expressed respectively by kd760(CH3NO2) = 2.94 ×1055T–12.6exp(−35500/T) s–1and kd∞(CH3NO2) = 5.88 × 1024T–2.35exp(−31400/T) s–1. In the low pressure limit, thedecomposition reaction takes place exclusively via the roaming TSproducing internally excited CH3ONO, giving rise to bothCH3O + NO and CH2O + HNO with the second-orderrate constant kd0(CH3NO2) = 1.17 × 1031T–10.94exp(−32400/T)cm3molecule–1s–1.For CH3ONO decomposition, a new roaming transition stateconnecting to the CH2O + HNO products has been located,lying 6.8 kcal/mol below the well-known four-member ring tight transitionstate and 0.7 kcal/mol below CH3O + NO. The rate constantspredicted by similar calculations give rise to the following expressionsfor the thermal decomposition of CH3ONO in He: kd760(CH3ONO) = 8.75 ×1041T–8.97exp(−22600/T) s–1and kd∞(CH3ONO) = 1.58 × 1023T–2.18exp(−21100/T) s–1in the temperature range 300–3000K. These results are in very good agreement with available experimentaldata obtained under practical pressure conditions. The much differentbranching ratios for the formation of CH3O + NO and CH2O + HNO in the decomposition of both CH3NO2and CH3ONO are also given in this work. [ABSTRACT FROM AUTHOR]

The thermal decomposition of C2H5OH highly diluted in Ar (1 and 3 ppm) has been studied by monitoring H atoms using the atomic resonance absorption spectrometry (ARAS) technique behind reflected shock waves over the temperature range 1450-1760 K at fixed pressure: 1, 1.45, and 2 atm. The rate constant and the product branching fractions have been determined by analyzing temporal profiles of H atoms; the effect of the secondary reactions on the results has been examined by using a detailed reaction mechanism composed of 103 elementary reactions. The apparent rate constant of ethanol decomposition can be expressed as k1/s-1 = (5.28 ± 0.14) x 1010[-(23 530 ± 980)/T] (T = 1450-1670 K, P = 1-2 atm) without a detectable pressure dependence within the tested pressure range of this study. Branching fractions for producing CH3 + CH2OH (1a) and H2O + C2H4(1b) have been examined by a quantitative measurement of H atoms produced in the successive decompositions of the products CH2OH (1a): the pressure dependence of the branching fraction for channel la is obtained by a linear least-squares analysis of the experimental data and can be expressed as Φ1a = (0.71 ± 0.07) - (826 ± 116)/T, (0.92 ± 0.04) - (1108 ± 70)/T, and (1.02 ± 0.10) - (1229 ± 168)/T for T= 1450-1760 K, at P = 0.99, 1.45, and 2.0 atm, respectively. The rate constant obtained in this study is found to be consistent with previous theoretical and experimental results; however, the pressure dependence of the branching fraction obtained in this study is smaller than those of previous theoretical works. Modification of the parameters for the decomposition rate in the falloff region is suggested to be important to improve the practical modeling of the pyrorysis and combustion of ethanol. [ABSTRACT FROM AUTHOR]