Methanol oxidation on the PtPd(111) alloy surface: A density functional theory study

The mechanisms of methanol (CH₃OH) oxidation on the PtPd(111) alloy surface were systematically investigated by using density functional theory calculations. The energies of all the involved species were analyzed. The results indicated that with the removal of H atoms from adsorbates on PtPd(111) surface, the adsorption energies of (i) CH₃OH, CH₂OH, CHOH, and COH increased linearly, while those of (ii) CH₃OH, CH₃O, CH₂O, CHO, and CO exhibited odd‐even oscillation. On PtPd(111) surface, CH₃OH underwent the preferred initial C H bond scission followed by successive dehydrogenation and then CHO oxidation, that is, CH₃OH → CH₂OH → CHOH → CHO → CHOOH → COOH → CO₂. Importantly, the rate‐determining step of CH₃OH oxidation was found to switch from CO → CO₂ on Pt(111) to COOH → CO₂ + H on PtPd(111) with a lower energy barrier of 0.96 eV. Moreover, water also decomposed into OH more easily on PtPd(111) than on Pt(111). The calculated results indicate that alloying Pt with Pd could efficiently improve its catalytic performance for CH₃OH oxidation through altering the primary pathways from the CO path on pure Pt to the non‐CO path on PtPd(111).     

Reactions of methyl radicals with acetaldehyde and acetaldehyde-d1. II. BEBO calculations of the temperature dependence of the rate constants

The BEBO method was used to calculate the kinetic isotope effect for formyl-hydrogen abstraction from acetaldehyde by methyl radicals. The calculated isotope effect and experimental ratios of the rate constants obtained at 785°K for the reactions of CH₃ with CH₃CHO and CH₃CDO, together with the theoretical temperature dependence of the specific rates (as formulated by the BEBO theory), were used to obtain rate constants for the steps CH₃ + CH₃CHO → CH₄ + CH₃CO (2a), CH₃ + CH₃CHO → CH₄ + CH₂CHO (2b), and CH₃ + CH₃CDO → CH₃D + CH₃CO (1a) between 298 and 1224°K. It was shown that the curvature apparent in the Arrhenius plot of the rate coefficient k₂ reported for the reaction of methyl radicals with acetaldehyde in the temperature range of 298–1224°K is caused both by the simultaneous contribution of steps (2a) and (2b) to methane formation, and by the curvature in the Arrhenius plots of the two elementary rate constants themselves. The predicted curve agrees well with the experimental data, especially if the tunneling correction is applied.     

Experimental and kinetic modeling study of the effect of sulfur dioxide on the mutual sensitization of the oxidation of nitric oxide and methane

New experimental results were obtained for the mutual sensitization of the oxidation of NO and methane in a fused silica jet‐stirred reactor operating at 10⁵ Pa, over the temperature range 800–1150 K. The effect of the addition of sulfur dioxide was studied. Probe sampling followed by online FTIR analyses and off‐line GC‐TCD/FID analyses allowed the measurement of concentration profiles for the reactants, stable intermediates, and final products. A detailed chemical kinetic modeling of the present experiments was performed. An overall reasonable agreement between the present data and modeling was obtained. According to the present modeling, the mutual sensitization of the oxidation of methane and NO proceeds via the NO to NO₂ conversion by HO₂ and CH₃O₂. The conversion of NO to NO₂ by CH₃O₂ is more important at low temperatures (800 K) than at higher temperatures (850–900 K) where the production of NO₂ is mostly due to the reaction of NO with HO₂. The NO to NO₂ conversion is favored by the production of the HO₂ and CH₃O₂ radicals yielded from the oxidation of the fuel. The production of OH resulting from the oxidation of NO accelerates the oxidation of the fuel: NO + HO₂ → OH+ NO₂ followed by OH + CH₄→ CH₃. In the lower temperature range of this study, the reaction further proceeds via CH₃ + O₂→ CH₃O₂; CH₃O₂+ NO → CH₃O + NO₂. At higher temperatures, the production of CH₃O involves NO₂: CH₃+ NO₂→ CH₃O. This sequence of reactions is followed by CH₃O → CH₂O + H; CH₂O +OH → HCO; HCO + O₂ → HO₂ and H + O₂ → HO₂ → CH₂O + H; CH₂O +OH → HCO; HCO + O₂ → HO₂ and H + O₂ → HO₂. The data and the modeling show that unexpectedly, SO₂ has no measurable effect on the kinetics of the mutual sensitization of the oxidation of NO and methane in the present conditions, whereas it frequently acts as an inhibitor in combustion. This result was rationalized via a detailed kinetic analysis indicating that the inhibiting effect of SO₂ via the sequence of reactions SO₂+H → HOSO, HOSO+O₂ → SO₂+HO₂, equivalent to H+O₂?HO₂, is balanced by the reaction promoting step NO+HO₂ → NO₂+OH. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 406–413, 2005     

Experimental measurements and kinetic modeling of CO/H2/O2/NOx conversion at high pressure

This paper presents results from lean CO/H₂/O₂/NO_x oxidation experiments conducted at 20–100 bar and 600–900 K. The experiments were carried out in a new high‐pressure laminar flow reactor designed to conduct well‐defined experimental investigations of homogeneous gas phase chemistry at pressures and temperatures up to 100 bar and 925 K. The results have been interpreted in terms of an updated detailed chemical kinetic model, designed to operate also at high pressures. The model, describing H₂/O₂, CO/CO₂, and NO_x chemistry, is developed from a critical review of data for individual elementary reactions, with supplementary rate constants determined from ab initio CBS‐QB3 calculations. New or updated rate constants are proposed for important reactions, including OH + HO₂ ? H₂O + O₂, CO + OH ? [HOCO] ? CO₂ + H, HOCO + OH ? CO + H₂O₂, NO₂ + H₂ ? HNO₂ + H, NO₂ + HO₂ ? HONO/HNO₂ + O₂, and HNO₂(+M) ? HONO(+M). Further validation of the model performance is obtained through comparisons with flow reactor experiments from the literature on the chemical systems H₂/O₂, H₂/O₂/NO₂, and CO/H₂O/O₂ at 780–1100 K and 1–10 bar. Moreover, introduction of the reaction CO + H₂O₂ → HOCO + OH into the model yields an improved prediction, but no final resolution, to the recently debated syngas ignition delay problem compared to previous kinetic models. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 40: 454–480, 2008     

High-temperature pyrolysis of acetaldehyde

High-temperature (>1000°K) pyrolysis of acetaldehyde (～1% in an atmosphere of pure nitrogen) was examined in a turbulent flow reactor which permits accurate determination of the spatial distribution of the stable species. Results show that the products in order of decreasing importance are CO, CH₄, H₂, C₂H₆, and C₂H₄. Rates of formation were consistent with the Rice–Herzfeld mechanism by including reactions to explain C₂H₄ formation and the possible presence of ketene. A steady-state treatment of the complete mechanism indicates that the overall reaction order decreases from \documentclass{article}\pagestyle{empty}\begin{document}$ \frac{3}{2} $\end{document} to 1, which is supported by the new experimental data. Using earlier low-temperature results, the rate constant for the reaction CH₃CHO → CH₃ + CHO (1) was found as k₁=10^15.85±0.21 exp (?81,775±1000/RT) sec^?1. Also, data for the ratio of rate constants for reactions CH₃CHO + CH₃ → CH₄ + CH₃CO (4) and 2CH₃ → C₂H₆(6) were fitted to the empirical expression k₄/k₆^1/2=10^?13.89±0.03T^6.1 exp(?1720±70/RT) (cm³/mole·sec)^1/2 and causes for the curvature are discussed. The noncatalytic effect of oxygen on acetaldehyde pyrolysis at high temperature is explained.     

A Theoretical Investigation of the Decomposition Reactions of Ethyl Formate in the S0 State

This study revisits the stability of the possible conformations and the decomposition reactions of ethyl formate in the S₀ state using the (U)MP2, MP4SDTQ, CCSD(T), and (U)B3LYP methods with various basis sets. The transition states of the decomposition channels to HCOOH + C₂H₄, CO + CH₃CH₂OH, CH₂O + CH₃CHO, HCOH + CH₃CHO, C₂H₆ + CO₂, and H₂ + CH₂CHOCHO are determined. The microcanonical rate constants derived from the RRKM theory are calculated for each of the decomposition reactions. The high‐pressure limit rate constants are calculated for the decomposition channels to HCOOH + C₂H₄, CO + CH₃CH₂OH, and CH₂O + CH₃CHO.     

FTIR spectroscopic study of the Cl- and Br-atom initiated oxidation of ethene

The reaction mechanism of the halogen (Cl and Br)-atom initiated oxidation of C₂H₄ was studied using the long path FTIR spectroscopic method in 700 torr of air at 296 ± 2 K. Among the major halogen-containing products were X? CH₂CHO, X? CH₂CH₂OH, and X? CH₂CH₂OOH (X = Cl or Br) which were shown to be formed via the self-reaction of the X? CH₂CH₂OO radicals, i.e., 2X? CH₂CH₂OO → 2X? CH₂CH₂O + O₂; (a) 2X? CH₂CH₂OO → X? CH₂CHO + X? CH₂CH₂OH + O₂ and (b) followed by X? CH₂CH₂O + O₂ → X? CH₂CHO + HO₂ and X? CH₂CH₂OO + HO₂ → X? CH₂CH₂OOH + O₂. From the observed yields of X? CH₂CHO and X? CH₂CH₂OH the branching ratios for reactions (a) and (b) were determined to be k_a/k_b = 1.35 ± 0.07(2σ) for both X = Cl and Br. In addition, the O₂-dependence of the rate constant for the Br + C₂H₄ reaction was determined by the relative rate technique as a function of O₂ partial pressure from 140 to 700 torr at 700 torr total pressure of N₂/O₂ diluent. Rate constants for the reactions of Cl-atoms with Cl-CH₂CHO and Br-atoms with Br-CH₂CHO were also determined to be [4.3 ± 0.2(2sigma;)] × 10^?11 and less than or equal to [1.83 ± 0.11(2σ)] × 10^?13 cm³ molecule^?1 s^?1, respectively.     

The decomposition of ethanol vapour by infrared radiation from a pulsed HF-laser

The decomposition of ethanol vapour induced by infrared radiation from a pulsed HF-laser has been studied as a function of pressure. At high pressures, above 10 torr, the main primary processes appear to be:C₂H₅OH → H₂ + CH₃CHO,C₂H₅OH → C₂H₄ + H₂O,C₂H₅OH → CH₃ + CH₂OHin a ratio of 3:2:1 which is independent of pressure. At low pressures the process yielding C₂H₄ and H₂O becomes dominant. The results suggest that the high pressure behaviour involves a “thermal” decomposition with collisional processes dominating, whereas at low pressures the decomposition is due to multiple photon absorption which at the lowest pressures approaches a collision-free unimolecular decomposition.     

Unusual H2-forming chain reaction in the 3130-Å photolysis of formaldehyde-oxygen mixtures at 25°C

A kinetic study has been made of the 3130-Å photolysis of CH₂O (8 torr) in O₂-containing mixtures (0.02–8 torr) and in the presence of added CO₂ (0–300 torr) at 25°C. Quantum yields of formation of H₂, CO, and CO₂ and the loss of O₂ were measured. Φ and Φ_CO were much above unity. In an explanation of these unexpected results, a new H-atom-forming chain mechanism was postulated involving HO₂ and HO addition to CH₂O: CH₂O + hν → H + HCO (1) H + CH₂O → H₂ + HCO (3) H + O₂ + M → HO₂ + M (6) HCO + O₂ → HO₂ + CO (8) HO₂ + CH₂O → (HO₂CH₂O) → HO + HCO₂H (15) HO + CH₂O → H₂O + HCO? (16); HCO? → H + CO (19) HO + CH₂O → H₂O + HCO (17) and HO + CH₂O → HCO₂H + H (18). When the results are rationalized in terms of this mechanism, the data suggest k₁₆ ? k₁₇ and k₁₆/k₁₈ ? 0.5. The data require that a reassessment of the relative rates of reactions (7) and (8) be made, since in the previous work HCO₂H formation was used as a monitor of the rate of reaction (7) HCO + O₂ + M → HCOO₂ + M (7). The present data from experiments at P = 8 torr and P = 1–4 torr give k₇[M]/(k₇[M] + k₈) ≥ 0.049 ± 0.017. These data coupled with the k₈ estimates of Washida and coworkers give k₇ ≥ (4.4 ± 1.6) × 10¹¹ l²/mol²·sec for M = CH₂O. The reaction sequence proposed here is consistent with the observed deterimental effect of O₂ addition on the laser-induced isotope enrichment in HDCO. In additional studies of CH₂O-O₂-isobutene mixtures it was found that Φ was equal to ?₂ as estimated in O₂-free CH₂O-isobutene mixtures. These results suggest that the increase in CO (ν = 1) product observed with O₂ addition in CH₂O photolysis does not result from perturbations in the fragmentation pattern of the excited CH₂O, but it is likely that it originates in the occurrence of the exothermic reaction HCO + O₂ → HO₂ + CO (ν = 1).     

Flow reactor studies of methyl radical oxidation reactions in methane‐perturbed moist carbon monoxide oxidation at high pressure with model sensitivity analysis

New rate constant determinations for the reactions CH₃ + HO₂ → CH₃O + OH (1) CH₃ + HO₂ → CH₄ + O₂ (2) CH₃ + O₂ → CH₂O + OH (3) were made at 1000 K by fitting species profiles from high‐pressure flow reactor experiments on moist CO oxidation perturbed with methane. These reactions are important steps in the intermediate‐temperature burnout of hydrocarbon pollutants, especially at super‐atmospheric pressure. The experiments used in the fit were selected to minimize the uncertainty in the determinations. These uncertainties were estimated using model sensitivity coefficients, derived for time‐shifted flow reactor experiments, along with literature uncertainties for the unfitted rate constants. The experimental optimization procedure significantly reduced the uncertainties in each of these rate constants over the current literature values. The new rate constants and their uncertainties were determined to be, at 1000 K: k₁ = 1.48(10)¹³ cm³ mol⁻¹ s⁻¹ (UF = 2.24) k₂ = 3.16(10)¹² cm³ mol⁻¹ s⁻¹ (UF = 2.89) k₃ = 2.36(10)⁸ cm³ mol⁻¹ s⁻¹ (UF = 4.23) There are no direct and few indirect measurements of reactions ( 1 ) and ( 2 ) in the literature. There are few measurements of reaction ( 3 ) near 1000 K. These results therefore represent an important refinement to radical oxidation chemistry of significance to methane and higher alkane oxidation. The model sensitivity analysis used in the experimental design was also used to characterize the mechanistic dependence of the new rate constant values. Linear sensitivities of the fitted rate constants to the unfitted rate constants were given. The sensitivity analysis was used to show that the determinations above are primarily dependent on the rate constants chosen for the reactions CH₃ + CH₃ + M → C₂H₆ + M and CH₂O + HO₂ → HCO + H₂O₂. Uncertainties in the rate constants of these two reactions are the primary contributors to the uncertainty factors given above. Further reductions in the uncertainties of these kinetics would lead to significant reductions in the uncertainties in our determinations of k₁, k₂, and k₃. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 75–100, 2001     

Kinetics and mechanism associated with the reactions of hydroxyl radicals and of chlorine atoms with 1‐propanol under near‐tropospheric conditions between 273 and 343 K

Rate constants for the reactions of OH radicals and Cl atoms with 1‐propanol (1‐C₃H₇OH) have been determined over the temperature range 273–343 K by the use of a relative rate technique. The value of k(Cl + 1‐C₃H₇OH) = (1.69 ± 0.19) × 10^?12 cm³ molecule^?1 s^?1 at 298 K and shows a small increase of 10% between 273 and 342 K. The value of k(OH + 1‐C₃H₇OH) increases by 14% between 273 and 343 K with a value of (5.50 ± 0.55) × 10^?12 cm³ molecule^?1 s^?1 at 298 K, and further when combined with a single independent experimentally determined value at 753 K gives k(OH + 1‐C₃H₇OH) = 4.69 × 10^?17T^1.8 exp(422/T) cm³ molecule^?1 s^?1, which fits each data point to better than 2%. Two well‐established structure–activity relationships for H abstraction by OH radicals give accurate predictions of the rate constant for OH + 1‐C₃H₇OH, provided the β‐CH₂ group is given an increased reactivity of a factor of about 2 over that for the structurally equivalent CH₂ group in alkanes at 298 K. A quantitative product analysis was carried out at 298 K for the Cl‐initiated photooxidation of 1‐C₃H₇OH, using both FTIR and gas chromatography. HCHO, CH₃CHO, and C₂H₅CHO were the only major organic primary products observed, although HCOOH was found in much smaller amounts as a secondary product. A key characteristic of the analysis was that the initial values of the product ratio [CH₃CHO]/[C₂H₅CHO] were effectively constant for NO pressures between 0.15 and 0.3 Torr, but fell by about 35% as the pressure fell to 0.0375 Torr. From a detailed consideration of the mechanism for the oxidation, it is suggested that C₂H₅CHO, CH₃CHO (+HCHO), and 3 molecules of HCHO are formed uniquely from CH₃CH₂CHOH, CH₃CHCH₂OH, and CH₂CH₂CH₂OH radicals, respectively. On this basis, use of the product yields gives the branching ratios of 56, 30, and 14% for Cl atom reaction at the α‐, β‐, and γ‐C? H positions in 1‐C₃H₇OH at 298 K. Given the very low temperature coefficients involved, little change will occur over tropospheric temperature ranges. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 110–121, 2002     

The Formation of OH*(<Superscript>2</Superscript>Σ<Superscript>+</Superscript>) Radical in the Reaction of Hydrogen with Oxygen behind a Shock Wave in Nonequilibrium Conditions

The mechanism of formation of the electronically excited radical OH*(A²Σ⁺) has been studied by analyzing calculations quantitatively describing the results of shock wave experiments carried out in order to determine the moment of maximum OH* radiation at temperatures T < 1500 K and pressures P ≤ 2 atm in the H₂ + O₂ mixtures diluted by argon when the vibrational nonequilibrium is a factor determining the mechanism and rate of the overall process. In kinetic calculations, the vibrational nonequilibrium of the initial H₂ and O₂ components, the HO₂, OH(X²Π), O₂*(¹Δ) intermediates, and the reaction product H₂O were taken into account. The analysis showed that under these conditions the main contribution to the overall process of OH* formation is caused by the reactions OH + Ar → OH* + Ar, H₂ + HO₂ → OH* + H₂O, H₂ + O*(¹D) → OH* + H, HO² + O → OH* + O² and H + H²O → OH* + H², which occur in the vibrational nonequilibrium mode (their activation barrier is overcome due to the vibrational excitation of reactants), and by H + O₃ → OH* + O₂ and H + H₂O₂ → OH* + H₂O, which are reverse to the reactions of chemical quenching.     

The role of the cage dimer of formaldehyde in the photolysis of formaldehyde: Argon matrix at 12 K

Photolysis of H₂CO was carried out in an Ar matrix with different matrix ratios (M/R). The infrared (IR) absorption spectra of the initial matrix preparation show that the matrix isolated monomers are almost exclusively present at very high dilutions (M/R or 5000) whereas the cage dimers and higher multimers are present in significant amounts at lower dilutions. The post-photolysis IR spectra indicate that the photodecomposition of H₂CO is mainly effected with the cage dimer, and that CH₃OH and CO are formed as photoproducts. The majority of the photoproducts exist as cage dimers of CH₃OH/CO. Upon thermal annealing after photolysis, diffusion through the matrix leads to the additional formation of aggregates composed of CH₃OH/H₂CO as well as CH₃OH/CO.     

The effect of temperature on formaldehyde photooxidation in oxygen-lean atmospheres

The photooxidation of formaldehyde in CH₂O? O₂, oxygen-lean mixtures was studied in the temperature range 298–378 K. H₂ and CO formation and the loss of O₂ proceed by a chain mechanism, which between 328 and 378 K follows the previously suggested kinetics [1] with one modification. The reaction HO₂ + CH₂O ? HO₂CH₂O (5) is now assumed to be reversible and ΔH is estimated to be between 14 and 19 kcal/mol. The relative yields of the chain formed H₂ and CO and of the consumed O₂ remained constant over the entire temperature range indicating that the relative efficiencies of the HO reactions: HO + CH₂O → H₂O HCO? (7), HO + CH₂O → H₂O + HCO (8) and HO + CH₂O → HOCH₂O (9) are temperature independent.     

An FTIR study of the Cl-atom-initiated reaction of glyoxal

The kinetics and mechanism of Cl-atom-initiated reactions of CHO? CHO were studied using the FTIR detection method to monitor the photolysis of Cl₂–CHO? CHO mixtures in 700 torr of N₂–O₂ diluent at 298 ± 2 K. The observed product distribution in the [O₂] pressure of 0–700 torr combined with relative rate measurements provide evidence that: (1) the primary step is Cl + CHO? CHO → HCl + CHO? CO with a rate constant of [3.8 ± 0.3(σ)] × 10^?11 cm³ molecule^?1 s^?1; (2) the primary product CHO? CO unimolecularly dissociates to CHO and CO with an estimated lifetime of ≤ca. 1 × 10^?7 s; (3) alternatively, the CHO? CO reacts with O₂ leading to the formation of CO, CO₂, and most likely the HO radical, but no stable products containing two carbon atoms; (4) the HO₂ radical, formed in the secondary reaction CHO + O₂ → HO₂ + CO, reacts with the CHO? CHO with a rate constant ca. 5 × 10^?16 cm³ molecule^?1 s^?1 to form HCOOH and a new transient product resembling that detected previously in the HO₂ reaction with HCHO.     

Reactions of primary and secondary butoxy radicals in oxygen at atmospheric pressure

The reaction pathways of n-butoxy and s-butoxy radicals have been investigated by TLC and HPLC analysis of end products, particularly peroxides and carbonyl compounds. The butoxy radicals were produced by the pyrolysis of very low concentrations of the corresponding dibutylperoxide in an atmosphere of oxygen and nitrogen, at atmospheric pressure. The decomposition reaction (3) s-BuO → C₂H₅ + CH₃CHO and the reaction (2) s-BuO + O₂ → HO₂ + CH₃COC₂H₅ have been studied, and the ratio k₃/k₂ has been determined in the temperature range 363–503 K by kinetic modeling of the formation of the observed acetaldehyde and methylethylketone. The rate constant k₃ obtained was: A good agreement was observed between experimental data and RRKM theory. The implications of the results for atmospheric chemistry and combustion are discussed. At room temperature, the reaction with O₂, yielding HO₂ radicals and methylethylketone is, by far, the main channel for s-BuO radicals. In the field of low temperature combustion, the decomposition of s-BuO radicals producing C₂H₅ and CH₃CHO is the main pathway; the route s-BuO + O₂ decreases tremendously in importance as the temperature is raised above 393 K.     

CO hydrogenation on stepped Cu and CuZn alloy surfaces: Competition between methanol synthesis and methanation pathways

Comprehensive fundamental understanding of CO hydrogenation reactions over Cu and ZnCu alloy surfaces is of great importance. Herein, we report a comparative DFT calculation study of elementary surface reaction network of CO hydrogenation reactions on stepped Cu(211), Cu(611), ZnCu(211) and ZnCu(611) surfaces. On ZnCu(211) and ZnCu(611) surfaces, the energetic favorable reaction path of CO hydrogenation reaction follows CO* → HCO* → H₂CO* → H₃CO* → CH₃OH* → CH₃OH with H₃CO* hydrogenation as the rate-limiting step and proceeds more facilely on ZnCu(611) surface than on ZnCu(211) surface. On Cu(211) and Cu(611) surfaces, the energetic favorable reaction path of CO hydrogenation reaction follows CO* → HCO* → HCOH* → H₂COH* → H₃COH* → CH₃* → CH₄* → CH₄ with H₂COH* hydrogenation as the rate-limiting step and proceeds more facilely on Cu(611) than on Cu(211). The key difference of CO hydrogenation reaction on ZnCu alloy surface and Cu is that the resulting CH₃OH* species desorbs to produce CH₃OH on ZnCu alloy but undergoes H*-assisted decomposition to CH₃* and eventually to CH₄ on Cu surface. These results successfully unveil elementary surface reaction networks and structure sensitivity of Cu and ZnCu alloy-catalyzed CO hydrogenation reactions.     

Probing the pyrolysis of ethyl formate in the dilute gas phase by synchrotron radiation and theory

The thermal decomposition of the atmospheric constituent ethyl formate was studied by coupling flash pyrolysis with imaging photoelectron photoion coincidence (iPEPICO) spectroscopy using synchrotron vacuum ultraviolet (VUV) radiation at the Swiss Light Source (SLS). iPEPICO allows photoion mass-selected threshold photoelectron spectra (ms-TPES) to be obtained for pyrolysis products. By threshold photoionization and ion imaging, parent ions of neutral pyrolysis products and dissociative photoionization products could be distinguished, and multiple spectral carriers could be identified in several ms-TPES. The TPES and mass-selected TPES for ethyl formate are reported for the first time and appear to correspond to ionization of the lowest energy conformer having a cis (eclipsed) configuration of the O = C (H)– O – C (H₂)–CH₃ and trans (staggered) configuration of the O= C (H)– O – C (H₂)– C H₃ dihedral angles. We observed the following ethyl formate pyrolysis products: CH₃CH₂OH, CH₃CHO, C₂H₆, C₂H₄, HC(O)OH, CH₂O, CO₂, and CO, with HC(O)OH and C₂H₄ pyrolyzing further, forming CO + H₂O and C₂H₂ + H₂. The reaction paths and energetics leading to these products, together with the products of two homolytic bond cleavage reactions, CH₃CH₂O + CHO and CH₃CH₂ + HC(O)O, were studied computationally at the M06-2X-GD3/aug-cc-pVTZ and SVECV-f12 levels of theory, complemented by further theoretical methods for comparison. The calculated reaction pathways were used to derive Arrhenius parameters for each reaction. The reaction rate constants and branching ratios are discussed in terms of the residence time and newly suggest carbon monoxide as a competitive primary fragmentation product at high temperatures.     

The ultraviolet absorption spectra of the acetyl radical and the kinetics of the CH3 + CO reaction at room temperature

A continuum-absorption spectrum between 200 and 240 nm is assigned to the acetyl radical. Kinetic measurements using molecular modulation spectroscopy show for the reaction CH₃ + CO (+M) → CH₃CO + M the rate constants are (1.8 ± 0.2) × 10^?18 cm³ molecule^?1 s^?1 at 100 Torr and (6 ± 1) × 10^?18 at 750 Torr. The rate constant for acetyl combination 2CH₃CO → (CH₃CO)₂ is (3.0 ± 10) × 10^?11 at 25°C.     

Gas‐phase reaction mechanism of Pd+ with CH3CHO: A density functional theoretical study

Details on the reactions of: (1) Pd⁺ + CH₃CHO → PdCO⁺ + CH₄ and (2) Pd⁺ + CH₃CHO → PdH + CH₃CO⁺ in the gas phase were investigated using density functional theory (B3LYP), in conjunction with the LANL2DZ+6‐311+G(d) basis set. Three encounter complexes were located on the potential energy surfaces and the calculations indicated that both the C? C and aldehyde C? H bond activation of acetaldehyde could lead to the dominant demethanation reaction. The charge transfer process for PdH abstraction was caused by an intramolecular PdH rearrangement of the newly found η¹‐aldehyde attached complex. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011