The vibrational relaxation of I2 by H2 in a supersonic jet

The vibrational relaxation of I₂ by H₂ has been studied in a supersonic free jet. It was observed that the addition of 5% H₂ to the helium carrier gas greatly reduces the concentration of X ¹Σ⁺_g(ν″ = 1) I₂ in the jet as compared to the concentration in a pure helium carrier. From this observation we have determined that the average vibrational relaxation cross sections of H₂ is 7.1 times as large as that of helium. Since the average vibrational relaxation cross section of deuterium is at least as large as that of hydrogen, the mechanism responsible for this phenomenon appears not to be dominated by mass effects.     

CH3NO2和CH3自由基吸氢反应途径和变分速率常数计算

采用MP2(full)/6-311G(d, p)从头算方法,优化了硝基甲烷和甲基自由基吸氢反应的过渡态结构,经QCISD(T)方法进行能量校正,得出该反应的正逆向反应的活化位垒分别是58.21 kJ•mol－1和67.17 kJ•mol－1.沿IRC分析指出该反应是氢转移协同反应,而且在反应途径上存在一个引导反应进行的振动模式,这一反应模式引导反应进行的区间在反应坐标S的-0.9～1.0(amu)1/2bohr之间;在温度为800～2600 K范围内,运用改进的变分过渡态理论(ICVT),计算了该反应的速率常数,并与实验类比所得的速率常数随温度的变化趋势进行了比较.     

Electronic and vibronic dipole moments of CH2D

Isotopic substitution of a hydrogen atom by deuterium turns a non-polar ion such as CH₃⁻ into a non-centrosymmetric system, CH₂D⁻, suitable for rotational spectra detection in space. The vibrational contribution to the dipole moment of the ion is investigated in this paper. The electronic potential surface has been obtained in a first-order CI, starting from a full valence active space built by using projected localized orbitals, to which core valence correlation effects have been added to account for rehybridization. The vibrational functions are obtained in a basis of harmonic oscillators. Three levels of vibrational treatment are presented, i.e. harmonic, non-coupled and coupled modes. The final result for the transition moment in the lowest vibrational level, μ_v = 0.327 Debye, shows that CH₂D⁻ should be observed and may be a useful tracer of CH₃⁺ in interstellar chemistry.     

The S1 ← S0 vibronic spectra and structure of the (CH3)2 CHCHO and (CH3)2 CHCDO 2-methylpropanal molecules

A multipass cell with an optical path up to 120 m long was used to measure the vibronic absorption spectra of 2-methylpropanal-h₁ (MPA-h₁, (CH₃)₂CHCHO)) and 2-methylpropanal-d₁ (MPA-d₁, (CH₃)₂CHCDO)) over the frequency range 28200–31600 cm⁻¹. The most intense spectral lines were assigned to transitions from vibrational levels of the cis and gauche MPA-h₁ and MPA-d₁ conformers in the ground electronic state (S ₀) to vibrational levels of conformers 1 and 3 in the lowest singlet excited electronic state (S ₁). According to our estimates, the origins (0 ₀ ⁰ ) of the 1 S ₁) ← cis(S ₀) and 3(S ₁) ← cis(S ₀) and also 1(S ₁) ← gauche(S ₀) and 3(S ₁) ← gauche(S ₀) electronic transitions were situated at 29147 and 29177, 29391 and 29417 cm⁻¹, respectively, for MPA-h₁ and at 29226 and 29240, 29480 and 29500 cm⁻¹ for MPA-d₁. The structure of conformers 1 and 3 in the S ₁ state was shown to differ from the structure of the cis and gauche conformers in the S ₀ state by the angle of rotation of the (CH₃)₂CH-isopropyl top and “pyramidal distortion” of the CCHO/CCDO carbonyl fragment. A series of fundamental frequencies of MPA conformers in different electronic states were found. The potential functions of inversion were determined for the conformer 1-conformer 3 pairs of MPA-h₁ and MPA-d₁ from the experimental energy levels of inversion vibrations. The potential barriers to inversion and equilibrium displacements of the CH/CD bond out of the CCO plane were found to be 735/675 cm⁻¹ and ±34°/±32° for MPA-h₁ and MPA-d₁, respectively. Original Russian Text ? I.A. Godunov, S.L. Lur’e, N.N. Yakovlev, V.A. Bataev, 2007, published in Zhurnal Fizicheskoi Khimii, 2007, Vol. 81, No. 1, pp. 52–62.     

Slow energy transfer between vibrational models of CH2Cl2, CD2Cl2, CH2ClBr and CH2Br2

Inefficient vibrational energy exchange between the lowest vibrational mode and the higher lying vibrational modes of CH₂Cl₂, CD₂Cl₂, CH₂ClBr and CH₂Br₂ was investigated by ultrasonic absorption experiments. Breathing sphere theory is used to interpret the data available for VV and VR, T transfer in methylene halides.     

An ab initio MO study on structures and energetics of CH2Si2, CH2Si2, and CH2Si2

The geometric structures and isomeric stabilities of various stationary points in CH₂Si₂ neutral, cation and anion are investigated at the coupled-cluster singles, doubles (triples) (CCSD(T)) level of theory. For the geometrical survey, the basis sets used are of the cc-pVTZ for the neutral and cation. The final energies are calculated by the use of the CCSD(T) level of theory with the aug-cc-pVTZ basis set at their optimized geometries. To the competitive two-anion isomers, the aug-cc-pVTZ basis sets are applied. The global minimum (N-1) of the CH₂Si₂ neutral has a quite different framework from those of the C₃H₂ (cyclopropenylidene) and Si₃H₂ (trisilacyclopropenylidene) neutrals. No competitive low-lying isomers are found in the CH₂Si₂ neutral. The attractive conformer (C-1) is predicted for the most stable cation, where its framework is quite different from that of the neutral N-1. Both H atoms are connected to the same C atom, but each C–H bond length is different from each other. Two competitive anion isomers with positive (real) electron affinities are predicted. The framework of the most stable anion A-1 is quite similar to that of the cation C-1, whereas both H atoms are equally connected to the same C atom. The framework of the anion isomer A-2 is the same as that in the neutral N-1. The vertical and adiabatic ionization potentials from the most stable neutral N-1 are 9.02 and 8.71 eV, respectively. The adiabatic electron affinity of the lowest lying isomer N-1 is only 0.43 eV and the vertical electron detachment energy form the global minimum anion (A-1) is 2.02 eV. The multi-centered Si–H–Si bonds are found in the neutral, cation, and anion.     

CH2+O2反应的反应机理

The mechanisms of the CH2＋ O2→ H2O＋ CO and CH2＋ O2→ H2＋ CO2 reactions have been studied by performing ab initio CAS(8,8)/6-31G(d,p) calculations, and five intermediates(IMn) and eight transitions(TSn) have been located along the reaction paths. The predicted path for the CH2＋ O2→ H2O＋ CO is: CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS4→ IM4a→ TS5→ H2O＋ CO. For the CH2＋ O2→ H2＋ CO2 reaction, there are two paths: (i) CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS6→ H2＋ CO2 and (ii) CH2＋ O2→ TS1→ IM1→ TS2→ IM2→ TS3→ IM3→ TS4→ IM4a→ TS7→ IM4b→ TS8→ H2＋ CO2, with the latter path more favorable energetically.     

Vibrational energy transfer in CH2F2

Infrared fluorescence has been observed from the ν₁, ν₆, 2ν₉, ν₈ and ν₄ levels of CH₂F₂ following excitation by a 9.6 μ Q-switch CO₂ laser. All the observed states exhibit a single exponential decay rate of approximately 44 msec^?1 torr^?1. The rare gas dependence of this rate has also been measured and found to be up to 20 times slower than the rate for the pure gas. Measurements of the risetimes of the observed fluorescence signals yielded an upper limit of 5 μsec at 1 torr for the ν₁, ν₆ and ν₈ levels. The 2ν₉ and ν₄ risetimes were effectively instantaneous under the experimental conditions that prevailed. The relative magnitudes of the measured rate are discussed in terms of existing V-T/R theories and collisional energy transfer processes.     

A rate constant for CH2(3B1) + CH3

Triplet methylene, CH₂(³B₁), and methyl radicals were produced by flash photolysis of a mixture of ketene and azomethane. A computer fit of the product ratios, using the known rate constants for CH₂ + CH₂, and CH₃ + CH₃, requires a rate constant of 5.0 × 10^?11 cm³ molecule^?1s^?1 for the reaction CH₂ + CH₃ ? C₂H₄ + H.     

Free energy of interchange between COO and CH3 or CH2 groups

The liquid—solid equilibrium temperatures in the binary systems between n-octacosane and methyl or ethyl octadecanoate are determined in order to obtain the interchange parameters between CH₃ or CH₂ and COO groups by means of the statistics of group interaction.     

Threshold energies for production of CH2(3B1) and CH2(1A1) from ketene photolysis. The CH2(3B1) ↔ CH2(1A1) energy splitting

By measuring the relative CO quantum yields from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25° for CH₂CO(¹A₁) → CH₂(³B₁) + CO(¹Σ⁺) to be 75.7 ± 1.0 kcal/mole. This corresponds to a value of 90.7 ± 1.0 kcal/mole for ΔH_f298⁰[CH₂(³B₁)]. By measuring the relative ratio of CH₂(¹A₁)/CH₂(³B₁) from ketene photolysis as a function of photolysis wavelength we have determined the threshold energy at 25°C for CH₂CO(¹A₁) → CH₂(¹A₁) + CO(¹Σ⁺) to be 84.0 ± 0.6 kcal/mole. This corresponds to a value of 99.0 ± 0.6 kcal/mole for ΔH_f298⁰[CH₂(¹A₁)]. Thus a value for the CH₂(³B₁) ? CH₂(¹A₁) energy splitting of 8.3 ± 1 kcal/mole is determined, which agrees with three other recent independent experimental estimates and the most recent quantum theoretical calculations.     

Carbonylvanadium complexes of the tripod ligands MeC(CH2PPh2)3 and P(CH2CH2PPh2)3

UV irradiation of [Et₄N] [V(CO)₆] in the presence of the tripod ligands (L) MeC(CH₂PPh₂)₃ (cp₃) and P(CH₂CH₂PPh₂)₃ (pp₃) yields [Et₄N] [V(CO)₅L], cis-[Et₄N] [V(CO)₄L] and mer-[Et₄N] [V(CO)₃L] (where the meridional configuration for L = cp₃ is uncertain). Except for [Et₄N] [V(CO)₅cp₃], all these species were isolated. The complexes are characterized by their IR, ³¹P and ⁵¹V NMR spectra.     

Synthesis and Characterization of a New Layered Aluminophosphate [Al3P4O16][(CH3)2NHCH2CH2NH(CH3)2][H3O]

A new layered aluminophosphate, denoted AlPO-CJ12, has been synthesized in the system Al(OPrⁱ)₃-H₃PO₄-tetramethylethylenediamine-triethyleneglycol and its structure solved by single-crystal X-ray diffraction analysis. It is further characterized by X-ray powder diffraction, ICP, TG, DTA, and elemental analyses. The compound has an empirical formula of [Al₃P₄O₁₆][(CH₃)₂NHCH₂CH₂NH(CH₃)₂][H₃O], and crystallizes in the triclinic space group P-1 (No. 2) with a=8.9907(6) Å b=9.8359(6) Å, c=14.5566(8) Å, α=75.872(3)°, β=88.616(3)°, γ=63.404(3)°, Z=2, R₁=0.0451, and wR₂=0.1094. The alternation of tetrahedral AlO₄ and PO₃ (=O) units forms a sheet structure with a 4×6×8 network. The inorganic layers stacked in an AAAA sequence are held together by the protonated organic amine and water molecules. The co-templating role of the water molecules is studied by the calculation of the nonbonding host-guest interaction energies through a computational simulation.     

The cleavage of tinallyl bonds in R2(CH2CHCH2)2Sn substrates as a route to organostannoxanes

Tetrabutyl-1,3-diacyloxydistannoxanes, (RCOO)Bu₂SnOSnBu₂(OOCR) (A) and/or tetrabutyl-1-acyloxy-3-hydroxydistannoxanes, (RCOO)Bu₂SnOSnBu₂(OH) (B), can be prepared from equimolecular amounts of dibutyldiallyltin and carboxylic acid, RCOOH (R = H, CH₃, CH₂Cl, CHCl₂, CCl₃, CF₃) in moist methanol or acetone/water (50/50, v/v). Isolation of compounds (A) or (B) depends upon the hydrolyzing power of the medium and the nature of R.     

反常蓝移单电子锂键Y…Li-CH3[Y=CH3, CH2CH3, CH(CH3)2, C(CH3)3]体系的结构与性质

在密度泛函理论B3LYP/6-311++G(d,p)及MP2/6-311++G(d,p)水平上研究了单电子锂键复合物Y…Li—CH3[Y=CH3, CH2CH3, CH(CH3)2, C(CH3)3]的结构与性质. 结果表明, 三种单电子锂键复合物H3CH2C…Li—CH3(II), (H3C)2HC…Li—CH3(III)和(H3C)3C…Li—CH3(IV)单电子锂键强度依II(-26.7 kJ·mol-1)相似文献   

Rate constant of unimolecular decomposition of the radical (CH3)2juvyCCH(CH3)2

The energy of activation of CH ₃ ^. radical rupture from the radical (CH₃)₂juvyCCH(CH₃)₂ is 142.2 kJ mol^–1; the selfcombination rate constant is k_c {(CH₃)₂juvyCCH(CH₃)₂}=10^7.3 dm³ mol^–1 s^–1.

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CH ₃ ^. (CH₃)₂juvyCCH(CH₃)₂ 142,2 /, k_c {(CH₃)₂juvyCCH(CH₃)₂}=10^{7,3 3–1 –1}.

     

The mechanism of SO2 oxidation by CH3O2 radicals. Rate coefficients for the reactions of CH3O2 with SO2 and NO

The reactions of CH₃O₂ with SO₂ and NO have been studied by steady state photolysis of azomethane in the presence of O₂SO₂→NO mixtures at 296 K and 1 atm total pressure. The quantum yield of NO oxidation by CH₃O₂ radicals is increased substantially when SO₂ is added to the system indicating an SO₂ induced chain oxidation of NO. The rate law gives k₁/k₂ = (2.5 ± 0.5) × 10^?3 for CH₃O₂ + SO₂ → CH₃O₂SO₂ (1), CH₃O₂ + NO → CH₃O + NO₂ (2). Combining this ratio with the absolute value of k₁ = 8.2 × 10^?15 cm³ s^?1 gives k₂ = 10^{?11.5 ± 02} cm³ s^?1.     

Theoretical calculational studies on the mechanism of thermal dissociations for RN3 (R=CH3, CH3CH2, (CH3)2CH, (CH3)3C)

Mechanisms of RN₃ (R=CH₃, CH₃CH₂, (CH₃)₂CH, (CH₃)₃C) dissociations are proposed based on CAS, MP2 and B3LYP methods. The energy gaps between the ground-state reactants RN₃ and the intersystem crossing (ISC) points are only a little lower than respective potential energy barriers of the spin-allowed reactions, ¹RN₃ → ¹RN + ¹N₂. The ISC point, therefore, is considered as a transition state of the spin-forbidden reactions, ¹RN₃ → ³RN + ¹N₂. The methods of IRC and topological analysis of electron density are used to explain and predict the thermal dissociation pathways of the reactions studied.