Chemical lasers produced from O(3P) atom reactions. V. CO laser emissions and vibrational population distribution in the flash-initiated SO2-CFBr3 system

CO laser emission at 5 μm was detected when SO₂ and CFBr₃ were flash photolyzed in the vacuum ultraviolet above 165 nm. Over 40 vibrational–rotational transitions ranging from Δv = 2 → 1 to 14 → 13, with the exception of those between 8 → 7 and 11 → 10, were identified. The CO emission is believed to result from the O + CF reaction: The vibrational population of the CO has been measured by means of a CO laser resonance absorption method. The CO was found to be vibrationally excited to v = 24 with a vibrational temperature of about 1.4 × 10⁴°K. The “surprisal analysis” of the observed CO distribution showed the possible occurrence of a minor process (presumably O + CFBr) that generated vibrationally colder CO. The effects of various additives on the CO emission were also examined. The addition of CO₂ to a D₂-SO₂-CFBr₃-He mixture resulted in a simultaneous osciallation at 3.6, 5, and 10.6 μm due to DF, CO, and CO₂, respectively. Additionally, the utilization of the O + CF_n (n = 1, 2, 3) reactions as F-atom sources for HF-laser operation in flash-initiated systems were demonstrated.     

DFT investigation of the mechanism of CH2CO + O(3P) reaction

A detailed theoretical survey of the potential energy surface (PES) for the CH₂CO + O(³P) reaction is carried out at the QCISD(T)/6‐311+G(3df,2p)//B3LYP/6‐311+G(d,p) level. The geometries, vibrational frequencies, and energies of all stationary points involved in the reaction are calculated at the B3LYP/6‐311+G(d,p) level. More accurate energy information is provided by single‐point calculations at the QCISD(T)/6‐311+G(3df,2p) level. Relationships of the reactants, transition states, intermediates, and products are confirmed by the intrinsic reaction coordinate (IRC) calculations. The results suggest that P1(CH₂+CO₂) is the most important product. This study presents highlights of the mechanism of the title reaction. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Photoexcitation and photodissociation lasers. III. mechanisms of CO laser emission from the vacuum UV photodissociation of CH2COO2 and CH2COSO2 mixtures

CO laser emission was detected in the vacuum UV flash photolysis of CH₂CO. The emission is attributed to the initial photodissociation reaction

Addition of O₂ to the CH₂CO system caused a pronounced enhancement in the laser intensity. This effect is believed to be due to the removal of the CH₂ + CH₂CO reaction, which produces uninverted CO molecules. A greater laser output was obtained when SO₂ was used instead of O₂. In the O₂-added system, a total of 16 transitions ranging from Δv(8→7) to (4→3) were identified. Addition of SO₂ increased the total number of lines to 34, lasing in the range between (11→10) and (4→3). This enhancement is ascribed to the occurrence of the reaction

In addition to these chemical effects, the effects of flash energy, inert gases and total pressures have been investigated.     

Mehrkernige Kobaltkomplexe. V. Präparative Herstellung von Tetrakis (äthylendiamin)-μ-peroxo-μ-amido- und μ-peroxo-μ-thiocyanatodikobalt (III)-Komplexen ausgehend von Tetrakis (äthylendiamin)bis-(ammin)-μ-peroxo-dikobalt (III)-tetraperchlorat

Polynuclear Cobalt Complexes. V. Preparation of tetrakis (ethylenediamine)-μ-peroxo-μ-amido and μ-peroxo-μ-thiocyanato-dicobalt (III) complexes starting from tetrakis (ethylenediamine)bis-(ammine)-μ-peroxo-dicobalt (III)-tetraperchlorate Racemic tetrakis (ethylenediamine)-μ-peroxo-μ-amido-dicobalt (III) thiocyanate and its corresponding hydroperoxo- and superoxo-complexes have been isolated from [(en)₂(NH₃)Co(O₂)(NH₃)(en)₂](ClO₄)₄. A new binuclear peroxo complex containing thiocyanate as bridging ligand was prepared by the same method. The stretching frequencies of the CN- and CS-group as well as the NCS-bending frequence in the IR. spectrum of [(en)₂Co(O₂, SCN)Co(en)₂](NO₃)₃ suggest that the μ-thiocyanato group is N-bonded (2050, 750, 475 cm^?1). A comparison of IR. spectra of known singly and doubly bridged μ-peroxo complexes is made. Characteristic absorption bands, assignable to ν(O? O) and ν(Co? O) are given.     

Quasiclassical trajectory study of the O(3P) + CH4 --> OH + CH3 reaction with a specific reaction parameters semiempirical Hamiltonian

We present a theoretical study of the O(3P) + CH4 --> OH + CH3 reaction using electronic structure, kinetics, and dynamics calculations. We calculate a grid of ab initio points at the PMP2/AUG-cc-pVDZ level to characterize the potential energy surface in regions of up to 1.3 eV above reagents. This grid of ab initio points is used to derive a set of specific reaction parameters (SRP) for the MSINDO semiempirical Hamiltonian. The resulting SRP-MSINDO Hamiltonian improves the quality of the standard Hamiltonian, particularly in regions of the potential energy surface beyond the minimum-energy reaction path. Quasiclassical-trajectory calculations are used to study the reaction dynamics with the original and the improved MSINDO semiempirical Hamiltonians, and a prior surface. The SRP-MSINDO semiempirical Hamiltonian yields OH rotational distributions in agreement with experimental results, improving over the results of the other surfaces. Thermal rate constants estimated with Variational Transition State Theory using the SRP-MSINDO Hamiltonian are also in agreement with experiments. Our results indicate that reparametrized semiempirical Hamiltonians are a good alternative to generating potential energy surfaces for accurate dynamics studies of polyatomic reactions.     

An FTIR spectroscopic study of the reactions Br + CH3CHO → HBr + CH3CO and CH3C(O)OO + NO2 ⇌ CH3C(O)OONO2 (PAN)

Based on an FTIR-product study of the photolysis of mixtures containing Br₂? CH₃CHO and Br₂? CH₃CHO? HCHO in 700 torr of N₂, the rate constant for the reaction Br + CH₃CHO → HBr + CH₃CO was determined to be 3.7 × 10^?12 cm³ molecule^?1 s^?1. In addition, the selective photochemical generation of Br at λ > 400 nm in mixtures containing Br₂? CH₃CHO? ¹⁴NO₂ (or ¹⁵NO₂)? O₂ was shown to serve as a quantitative preparation method for the corresponding nitrogen-isotope labeled CH₃C(O)OONO₂ (PAN). From the dark-decay rates of ¹⁵N-labeled PAN in large excess ¹⁴NO₂, the rate constant for the unimolecular reaction CH₃C(O)OO¹⁵NO₂ → CH₃C(O)OO + ¹⁵NO₂ was measured to be 3.3 (±0.2) × 10^?4 s^?1 at 297 ± 0.5 K.     

Vibrational distributions of the CO(v) products of the C2H2 + O(3P) and HCCO + O(3P) reactions studied by FTIR emission

The C2H2 + O(3P) and HCCO + O(3P) reactions are investigated using Fourier transform infrared (FTIR) emission spectroscopy. The O(3P) radicals are produced by 193 nm photolysis of an SO2 precursor or microwave discharge in O2. The HCCO radical is either formed in the first step of the C2H2 + O(3P) reaction or by 193 nm photodissociation of ethyl ethynyl ether. Vibrationally excited CO and CO2 products are observed. The microwave discharge experiment [C2H2 + O(3P)] shows a bimodal distribution of the CO(v) product, which is due to the sequential C2H2 + O(3P) and HCCO + O(3P) reactions. The vibrational distribution of CO(v) from the HCCO + O(3P) reaction also shows its own bimodal shape. The vibrational distribution of CO(v) from C2H2 + O(3P) can be characterized by a Boltzmann plot with a vibrational temperature of approximately 2400 +/- 100 K, in agreement with previous results. The CO distribution from the HCCO + O(3P) reaction, when studied under conditions to minimize other processes, shows very little contamination from other reactions, and the distribution can be characterized by a linear combination of Boltzmann plots with two vibrational temperatures: 2320 +/- 40 and 10 300 +/- 600 K. From the experimental results and previous theoretical work, the bimodal CO(v) distribution for the HCCO + O(3P) reaction suggests a sequential dissociation process of the HC(O)CO++ --> CO + HCO; HCO --> H + CO.     

Theoretical study on the reaction mechanism of(CH_3)_3CO+CO

The global environment pollution includes pho-tochemical smog, acid rain and stratospheric ozonedepletion. The short-lived species/radicals in atmos-phere are closely related to these phenomena. Theshort-lived species/radicals bring the photochemicalsmog,…     

A diode laser study of the Cl + CH3CO reaction

Real-time kinetic measurements are reported for the Cl + CH₃CO → CH₂CO + HCl reaction. The experiments utilize infrared spectroscopy to determine the time dependence of the ketene formed via this reaction and of the CO produced from the subsequent rapid reaction between chlorine atoms and ketene. The reaction is investigated over a pressure range of 10–200 torr and a temperature range of 215–353 K. Within experimental error the rate constant under these conditions is k_5a = (1.8 ± 0.5) × 10⁻¹⁰ cm³ s⁻¹. We have also examined the Cl + CH₂CO reaction and found it to have a rate constant of k₆ = (2.5 ± 0.5) × 10⁻¹⁰ cm³ s⁻¹ independent of temperature. © John Wiley & Sons, Inc. Int J Chem Kinet 29: 421–429, 1997.     

Thia- und Selena-arachno-undecaboran 6,7-μ-(CH3E)B10H13 Kristallstruktur von arachno-6,7-μ-(CH3Se)B10H13 Theoretische Untersuchungen der Molekülstrukturen und 11B-NMR-Verschiebungen von arachno-6,7-μ-(CH3E)B10H13

Thia- and Selena-arachno-undecaborane 6,7-μ-(CH₃E)B₁₀H₁₃. Crystal Structure of arachno-6,7-μ-(CH₃Se)B₁₀H₁₃. Theoretical Investigations of the Molecular Structures and ¹¹B NMR Shifts of arachno-6,7-μ-(CH₃E)B₁₀H₁₃ The reaction of B₁₀H₁₄ with (CH₃)₂S yields with loss of H₂ the base adduct 6,9-[(CH₃)₂S]₂B₁₀H₁₂. Although an analogous reaction between B₁₀H₁₄ with disulfanes or diselenanes was expected to produce 6,9 bridged dichalcogen derivatives, (CH₃)₂S₂ failed to react even under reflux conditions. Trisulfane (CH₃)₂S₃ does react, but the pathway is different and leads to (CH₃S)B₁₀H₁₃ 2 without loss of H₂. Unlike of (CH₃)₂S₂, (CH₃)₂Se₂ yields (CH₃Se)B₁₀H₁₃, 3 . Both 2 and 3 are formed by substitution of a bridging hydrogen and could be obtained in pure form and characterized ¹¹B NMR spectroscopically. A single crystal X-ray structure analysis also was performed on 3 (space group P2₁/c). The molecular structures of 2 and 3 were optimized at the MP2 level and ¹¹B NMR shifts were computed at the IGLO-SCF, GIAO-SCF and GIAO-B3LYP levels of theory.     

Crossed-beam dynamics studies of the radical-radical combustion reaction O((3)P) + CH3 (methyl)

The dynamics of the radical-radical reaction O((3)P) + CH(3), a prototypical case for the reactions of atomic oxygen with alkyl radicals of great relevance in combustion chemistry, has been investigated by means of the crossed molecular beam technique with mass spectrometric detection at a collision energy of 55.9 kJ mol(-1). The results have been examined in the light of previous kinetic and theoretical work. From product angular and velocity distribution measurements, the dynamics of the predominant H-displacement channel leading to formaldehyde formation has been characterized. This channel has been found to proceed via the formation of an osculating complex; a significant coupling between the product centre-of-mass angular and translational energy distributions has been noted. Experimental attempts to characterize the dynamics of the channel leading to HCO + H(2) have failed and it remains unclear whether HCO is formed by the reaction and/or, if formed, a part of HCO does not dissociate quickly into CO + H.     

Br+CH3S(O)CH3反应机理的直接动力学研究

采用直接动力学的方法，对多通道反应体系Br＋CH3S（O）CH3进行了理论研究．在BH＆H-LYP／6-311G（2d，2p）水平下获得了优化几何构型、频率及最小能量路径（MEP），能量信息的进一步确认在MC-QCISD（单点）水平下完成．利用正则变分过渡态理论，结合小曲率隧道效应校正（CVT／SCT）方法计算了该反应的两个可行的反应通道在200K～2000K温度范围内的速率常数．在整个反应区间内，生成HBr的反应通道与生成CHa的反应通道存在着竞争，前者是主反应通道，后者是次反应通道．变分效应和小曲率隧道效应对反应速率常数的计算影响都很小．理论计算得到的两个反应通道的反应速率常数与实验值符合得很好．     

Mass spectrometric study of μ4-oxohexa-μ-acetatotetrazinc,Zn4O(CH3CO2)6

The electron impact mass spectrum of Zn₄O(CH₃CO₂)₆ isostructural to Be₄O(CH₃CO₂)₆ studied earlier is reported. The principal fragmentation paths of both compounds involve the elimination of M(CH₃CO₂)₂ where M is Zn, Be, or (CH₃CO)₂O. Further fragmentations proceed by the losses of CH₂CO and H₂O. The spectrum of Zn₄O(CH₃CO₂)₆ contains intense doubly charged ions. The results obtained are interpreted in terms of stereochemical considerations.     

Exploring the dynamics of hydrogen atom release from the radical-radical reaction of O(3P) with C3H5

The gas-phase radical-radical reaction dynamics of O(3P) + C3H5 --> H(2S) + C3H4O was studied at an average collision energy of 6.4 kcal/mol in a crossed beam configuration. The ground-state atomic oxygen [O(3P)] and allyl radicals (C3H5) were generated by the photolysis of NO2 and the supersonic flash pyrolysis of allyl iodide, respectively. Nascent hydrogen atom products were probed by the vacuum-ultraviolet-laser induced fluorescence spectroscopy in the Lyman-alpha region centered at 121.6 nm. With the aid of the CBS-QB3 level of ab initio theory, it has been found that the barrierless addition of O(3P) to C3H5 forms the energy-rich addition complexes on the lowest doublet potential energy surface, which are predicted to undergo a subsequent direct decomposition step leading to the reaction products H + C3H4O. The major counterpart C3H4O of the probed hydrogen atom is calculated to be acrolein after taking into account the factors of barrier height, reaction enthalpy, and the number of intermediates involved along the reaction pathway. The nascent H-atom Doppler profile analysis shows that the average center-of-mass translational energy of the H + C3H4O products and the fraction of the total available energy released as the translational energy were determined to be 3.83 kcal/mol and 0.054, respectively. On the basis of comparison with statistical calculations, the reaction proceeds through the formation of short-lived addition complexes rather than statistical, long-lived intermediates, and the polyatomic acrolein product is significantly internally excited at the moment of the decomposition.     

Mechanistic and kinetic study of the CH3CO + O2 reaction

Potential-energy surface of the CH3CO + O2 reaction has been calculated by ab initio quantum chemistry methods. The geometries were optimized using the second-order Moller-Plesset theory (MP2) with the 6-311G(d,p) basis set and the coupled-cluster theory with single and double excitations (CCSD) with the correlation consistent polarized valence double zeta (cc-pVDZ) basis set. The relative energies were calculated using the Gaussian-3 second-order Moller-Plesset theory with the CCSD/cc-pVDZ geometries. Multireference self-consistent-field and MP2 methods were also employed using the 6-311G(d,p) and 6-311++G(3df,2p) basis sets. Both addition/elimination and direct abstraction mechanisms have been investigated. It was revealed that acetylperoxy radical [CH3C(O)OO] is the initial adduct and the formation of OH and alpha-lactone [CH2CO2(1A')] is the only energetically accessible decomposition channel. The other channels, e.g., abstraction, HO2 + CH2CO, O + CH3CO2, CO + CH3O2, and CO2 + CH3O, are negligible. Multichannel Rice-Ramsperger-Kassel-Marcus theory and transition state theory (E-resolved) were employed to calculate the overall and individual rate coefficients and the temperature and pressure dependences. Fairly good agreement between theory and experiments has been obtained without any adjustable parameters. It was concluded that at pressures below 3 Torr, OH and CH2CO2(1A') are the major nascent products of the oxidation of acetyl radicals, although CH2CO2(1A') might either undergo unimolecular decomposition to form the final products of CH2O + CO or react with OH and Cl to generate H2O and HCl. The acetylperoxy radicals formed by collisional stabilization are the major products at the elevated pressures. In atmosphere, the yield of acetylperoxy is nearly unity and the contribution of OH is only marginal.     

A gas-phase crossed-beam study of OH produced in the radical-radical reaction of O((3)P) with iso-propyl radical (CH3)2CH

The gas-phase radical-radical reaction dynamics of ground-state atomic oxygen [O((3)P)] with iso-propyl radicals, (CH(3))(2)CH, were investigated by applying a combination of high-resolution laser-induced fluorescence spectroscopy in a crossed-beam configuration and ab initio calculations. The nascent distributions of OH (X(2)Π: υ' = 0) from the major reaction channel O((3)P) + (CH(3))(2)CH → C(3)H(6) (propene) + OH showed substantial internal excitations with a bimodal feature of low- and high-N' components with neither spin-orbit nor Λ-doublet propensities. Unlike previous kinetic results, proposed to proceed only through the direct H-atom abstraction process, on the basis of the population analysis and comparison with the statistical theory, the title reaction can be described in terms of two competing mechanisms at the molecular level: direct abstraction process and indirect short-lived addition-complex-forming process with a ratio of 1.25?:?1.     

CH3CH2+O(3P)反应机理的理论研究

The reaction for CH3CH2+O(3P) was studied by ab initio method. The geometries of the reactants, intermediates, transition states and products were optimized at MP2/6-311+G(d,p) level. The corresponding vibration frequencies were calculated at the same level. The single-point calculations for all the stationary points were carried out at the QCISD(T)/6-311+G(d,p) level using the MP2/6-311+G(d,p) optimized geometries. The results of the theoretical study indicate that the major products are the CH2O＋CH3, CH3CHO+H and CH2CH2+OH in the reaction. For the products CH2O＋CH3 and CH3CHO+H, the major production channels are A1: (R)→IM1→TS3→(A) and B1: (R)→IM1→TS4→(B), respectively. The majority of the products CH2CH2+OH are formed via the direct abstraction channels C1 and C2: (R)→TS1(TS2)→(C). In addition, the results suggest that the barrier heights to form the CO reaction channels are very high, so the CO is not a major product in the reaction.