Monte Carlo simulation of O(1D) + H2 and O(1D) + HCl — rotational excitation of product OH radicals

Experimental studies with molecular beam and LIF techniques have independently shown that the reaction O(¹D) + H₂ → OH + H passes through a long-lived complex and gives products with small translational and large rotational excitation. We have previously published a statistical algorithm, based on ordinary RRKM theory with angular momentum restrictions included, which was designed to simulate molecular beam experiments. It has now been modified and applied to simulate the experimental rotational OH distributions from O(¹D)+H₂, measured by Luntz et al. The present study also includes simulation of similar results by Luntz for O(¹D) + HCI → OH + Cl. The purely statistical algorithm successfully simulates the apparently non-statistical experimental rotational distributions. For these reactions the total angular momentum conservation. which is applied at the transition state, proves to be decisive for the product energy distributions.     

Potential energy surfaces for the photodissociation H2O→O(1Dg + H2(X1Σ+g)

The minimum energy pathways for symmetrical dissociation of water into O(¹D_g + H₂(X¹Σ⁺_g) are calculated by the MRD Cl technique for various excited states of H₂O and possible mechanism for the photodissociation are discussed.     

Reactive scattering of O(1D) + H2

The angular and velocity distribution of OH product frorn the O(¹ D) + H₂ reaction at 2.7 $\text{kcal}\text{mole}$ collision energy has been obtained in a crossed molecular beam study. The product is found to be forward-backward symmetric; most of the reaction occurs through insertion of the oxygen to form ground electronic state H₂O.     

Energy partitioning in the reaction O(1D) + H2O → OH + OH. V. Rotational relaxation of OH(X2Π, ν″, J″)

The rotational relaxation of OH(X²Π, ν″, J″) in ν″, = 0, 1, and 2 produced from the reaction of O (¹D) with H₂O has been studied as a function of H₂O vapor pressure and added argon. Water molecules are extremely efficient in bringing about relaxation and the experiments performed indicate that, on the average, the high temperature distribution is relaxed to nearly room temperature at a gas kinetic rate. This observation is rationalized by assumming a collision complex between OH and H₂O having a quasichemical interaction similar to weak hydrogen bonding. The nascent OH internal energy distribution does not depend upon the translational energy of the O(¹D) reactant. Translational relaxation of the nascent OH product by H₂O is fast, as fast as rotational relaxation.     

Effect of curvature of the minimum energy path upon reaction dynamics: the H2O−(2B1)→H−(1S) + OH(2Π) dissociation

The dynamics of the H₂O^?(²B₁)→H^?(¹S) + OH(²Π) dissociation has been studied on three different potential energy surfaces using a quasiclassical trajectory method in the fixed-angle approximation. The partitioning of the excess energy between translational and internal energies of the fragments appears to be strongly affected by the curvature of the minimum-energy path.     

Sensitization of the OH(A 2Σ+ → X 2Πi) emission by Hg(6 3P0) metastables

The electronic energy transfer process Hg(6 ³P₀) + OH(X²Π_i, υ = 0,K) → Hg(6 ¹S₀) + OH(A ²Σ⁺, υ,K) has been studied by the sensitized fluorescence method. A rather broad spectrum of rotational population, N_υ′K′, was obtained under conditions of minimum relaxation, which illustrates the non-resonant and non-optical nature of this energy transfer process. The fractions of the exoergicity, above electronic excitation of OH(A ²Σ⁺, υ = 0, K = 0), going into vibrational, rotational and translational excitation are 0.11, 0.31, and 0.58, respectively. A statistical mode of energy partitioning, such as would result from long-lived complex formation, seems to account well for these observations.     

OH rotational quantum state distributions and relaxation efficiencies for the reaction system O(1D) + H2O → 2OH

The OH rotational distribution from O(¹D) + H₂O → 2OH is presented. The v' = 0 distribution corresponds to two Boltzmann distributions. ≈500 K (k = 1–6) and ≈2500 K (k ? 6). Rotational relaxation efficiencies for N₂, He, O₂ were ?0.1, ?0.1, ?0.4. More limited data are presented for the v' = 1 and 2 levels.     

Excitation of XeF* by reactions of XeF2 with Ar(3P0,2),Kr(3P2) and Xe(3P2)

The reactions of the lowest metastable states of Ar, Kr and Xe with XeF₂ were studied in a flowing afterglow apparatus; XeF emission (from D²Π_{$\text{1}\text{2}$} and B ²Π⁺ states) was observed in all cases. The total rate constants (cm³ molecule^?1 s^?1) for XeF^* formation were determined as 75 × 10^?11 ? Xe(³P₂);64 × 10^?11 ? Kr(³P₂) and 20 × 10^?11 ? Ar(³P_0,2). The reactions of Ar(³P_0,2) and Kr(³P₂) with XeF₂ also gave ArF^* and KrF^*, respectively. Analysis of these emissions indicates that at least two different mechanisms are operative: reactive quenching by the ionic—covalent curve-crossing mechanism and excitation transfer. The Ar(³P_0,2 + XeF₂ reaction is a sufficiently strong source of XeF(D—X) emission that the main features of the XeF(D²Π_{$\text{1}\text{2}$} ? X²Σ⁺) system could be photographed and tentative assignments of these vibrational bands are given. The XeF(D → B) emission could not be observed and the ratio of the D—X versus the D—B transition probability must be > 1000 : 1.     

Hydrothermal Synthesis, Single-Crystal Structure Analysis, and Solid-State NMR Characterization of Zn2(OH)0.14(3)F0.86(3)(PO4)

The zinc fluoro phosphate Zn₂F(PO₄) has been produced by hydrothermal synthesis employing hydrofluoric acid as a mineralizer in a H₂O or D₂O medium. A single-crystal X-ray synchrotron diffraction analysis of Zn₂F(PO₄) shows that the zinc fluoro phosphate is monoclinic, a=9.690(1), b=12.793(1), and c=11.972(1) Å, β=108.265(1)°, space group P2₁/c, No. 14, Z=16. Reflections hkl with k=2n+1 are weak but significant and the structure shows pseudosymmetry. Zn₂F(PO₄) has the wagnerite-type M₂F(XO₄) structure with four Zn atoms each coordinated to four O atoms and one F atom while four other Zn atoms are coordinated to four O atoms and two F atoms. A difference Fourier map, calculated from the single-crystal X-ray data, shows additional electron density close to the four fluorine atoms, indicating a possible partial substitution of F⁻ by OH⁻ ions. This is unambiguously confirmed by ³¹P-{¹H} cross-polarization magic-angle spinning (MAS) and by ¹H/²H MAS NMR spectroscopy. The narrow line width observed for the ¹H resonance and the unique set of ²H quadrupole coupling parameters (obtained for the Zn₂F(PO₄) sample using D₂O as medium) show that ¹H/²H is present as OH(D) groups rather than as water of crystallization in the structure. Quantitative ¹H MAS NMR analysis shows that the composition of the sample is Zn₂(OH)_0.14(3)F_0.86(3)(PO₄). The high-speed ¹⁹F MAS NMR spectrum exhibits two resolved resonances with equal intensity, which are ascribed to an overlap of resonances from the four distinct fluorine sites in Zn₂(OH)_0.14(3)F_0.86(3)(PO₄).     

On a simple reaction mechanism for the collision-induced dissociation He + Li2(B1Πu) → He + Li(2 2S) + Li(2 2P)

A simple reaction mechanism is suggested for the dissociation of electronically excited Li₂(B¹Π_u) in collision with rare-gas atoms. Experimental rate constants for dissociation of Li₂ in specific vibrational—rotational levels (ν1J) show an unexpected behaviour as a function of the initial molecular energy and angular momentum. We propose that raction proceeds by a transition to the ¹Π_g state of Li₂. This may dissociate more readily since it is more weakly bound and has a larger equilibrium distance than the ¹Π_u state.     

水在HfO2(111)和(110)表面的吸附与解离

运用广义梯度近似密度泛函理论方法(GGA-PW91)结合周期平板模型, 研究水分子在二氧化铪(111)和(110)表面不同吸附位置在不同覆盖度下的吸附行为. 通过比较不同吸附位的吸附能和几何构型参数发现:(111)和(110)表面铪原子(top 位)是活性吸附位. 水分子与表面的吸附能值随覆盖度的变化影响较小. 在(111)和(110)表面, 水分子都倾向以氧端与表面铪原子相互作用. 同时也计算了羟基、氧和氢在表面的吸附, Mulliken 电荷布居, 态密度及部分频率. 结果表明, 在两种表面羟基以氧端与表面铪相互作用, 氧原子与表面铪和氧原子同时成键, 而氢原子直接与表面氧原子相互作用形成羟基. 通过过渡态搜索, 水分子在(111)和(110)表面发生解离, 反应能垒分别为9.7和17.3 kJ·mol^-1, 且放热为59.9和47.6 kJ·mol^-1.     

Bending potentials for H2O in the ground and the first six singlet excited states

MRD CI calculations are presented for the bending potentials of H₂O in the ground and first six singlet excited states. The results are discussed with reference to the H(²S) + OH(A ²Σ⁺) dissociation path of H₂O.     

Correlation effects on energy curves for proton transfer. The cation [H5O2]+

Potential curves for proton transfer in [H₅O₂]⁺ and for the dissociation of one OH bond in [H₃O]⁺ were calculated by both ab initio and semi-empirical LCAO MO SCF CI methods. The energy barrier of the symmetric double minimum potential in [H₅O₂]⁺ is very sensitive to electron correlation. At an OO distance of 2.74 Å it decreases from the HF value of 9.5 kcal/mole to about 7.0 kcal/mole. The results of the semi-empirical calculations agree well with the ab initio data as long as only relative effects are regarded. The partitioning of correlation energy into contributions of individual electron pairs is very similar for proton transfer in [H₅O₂]⁺ and for the dissociation of one OH bond in [H₃O]⁺. In this example the proton transfer appears as a superposition of two “contracted ionic dissociation” processes. An interpretation of the behaviour of correlation during these processes is presented.     

氧分子在Cu2O(111)表面吸附与解离的理论研究

本文采用密度泛函方法结合周期性平板模型,研究了氧原子和氧分子在完整和存在缺陷的Cu₂O(111)表面的吸附。计算结果表明氧原子倾向于吸附在配位饱和的Cu_CSA位,而对于氧分子,则强烈倾向于吸附在配位不饱和的Cu_CUS位。氧分子在含有氧空位的缺陷表面的优势吸附位为平行吸附于空位上方的桥位。过渡态的计算表明氧分子在缺陷表面的解离是一个活化能很小的放热过程。     

Quasiclassical Trajectory Study of the Reaction of CD4 with O(1D)

Extensive quasiclassical trajectory calculations for the O(¹D)+CD₄ multichannel reaction were carried out on a new global potential energy surface fit by permutationally invariant polynomials. The product branching ratios, translational energy distributions, and angular distributions of OD+CD₃, D+CD₂OD/CD₃O, and D₂+DCOD/D₂CO product channels were calculated and compared with the available experimental results. Good agreement between theory and experiment has been achieved, indicating small isotope effects for the title reaction. The O(¹D)+CD₄ reaction mainly proceeds through the CD₃OD intermediate via the trapped abstraction mechanism, with initial abstraction of the D atom rather than the direct insertion, followed by decomposition of CD₃OD into various products.     

Thermally induced incomplete high-spin (5T2) ⇌ low-spin (1A1) transition in solid bis[2-(2-pyridylamino)-4-(2-pyridyl) thiazolato]iron (II)

The ⁵⁷Fe Mössbauer effect in two samples (A and B) of [Fe(papt)₂] and in its solvates with CHCl₃ and C₆H₆ has been studied between 4.2 and 343 K and clearly indicates a temperature induced high-spin (⁵T₂) ? low-spin (¹A₁) transition in these compounds [paptH = 2-(2-pyridylamino)-4-(2-pyridyl) thiazole]. At 343 K, sample B shows a doublet with ΔE_Q = 2.03 mm s^?1 and δIS = +0.87 mm s^?1, characteristic of a ⁵T₂ ground state. At 257 K, a second doublet, typical for a ¹A₁ ground state, is observed and its intensity increases as the transition progresses but levels off below ～ 100 K. At 4.2 K, 83% of the intensity is due to the ¹A₁ state, and ΔE_Q(¹A₁) = 1.56 mm s^?1 and δ^IS(¹A₁ = +0.32 mm s^?1. In an applied magnetic field, V_zz(¹A₁) < 0 and η ≈ 0.7 have been determined, whereas for the ^sT₂ ground state, V_zz(^sT₂) > 0, η ≈ 0.75, and an internal hyperfine field H_n ≈ ?13 kG have been observed. Similar results have been obtained with the other samples.Debye-Waller factors f5_T2 and f1_A1 were determined from the saturation corrected areas in the Mössbauer spectra, assuming Curie-Weiss dependence of the magnetic susceptibility for the ⁵T₂ and constant υ_cff for the ¹A₁ ground state. The temperature dependence of ?In f1_A1 closely follows the Debye model with Θ1_A1 = 165 K, whereas the same applies to ?ln f5_T2 only above ～ 210 K and Θ5_T2 = 134 K. The nature of the observed transition is discussed and the data presented are shown to be incompatible with a model based on a Boltzmann distribution between the two states.     

Theoretical study of the structure and stability of the heme dimer (FeC34H32N4O4)2 and its ion (FeC34H32N4O4) 2+

The electronic and geometric structures and the dissociation energies of the isolated molecule of heme dimer (heme)₂ = (FeC₃₄H₃₂O₄N₄)₂ and its ion (heme) ₂ ⁺ = (FeC₃₄H₃₂O₄N₄) ₂ ⁺ in the states with different multiplicities have been calculated by the density functional theory B3LYP method with the Gen-1 = 6-31G*(Fe) + 6-31G(C,H,N,O) and Gen-2 = 6-311++G*(Fe) + 6-31G*(C,H,N,O) basis sets. The computation results are compared with the analogous calculated data on monomeric heme and hemin⁺, as well as the previously considered dimeric ferriporphyrin X molecule and ion FeC₃₄H₃₁O₄N₄) ₂ ^{0, +} . In the heme dimer cation (heme) ₂ ⁺ , which is identified in mass spectra, the rings are linked with each other by a pair of Fe carbonyl bridges Fe⋯O_b = C(OH) and a pair of hydrogen bridges OH_b⋯N. According to the calculations, the most favorable state for (heme) ₂ ⁺ is the sextet in which five unpaired electrons are approximately uniformly distributed over the metal atoms, whereas the states with higher multiplicities 8 and 10 are, respectively, 0.15 and 0.20 eV higher on the energy scale. For the neutral dimer (heme)₂, the quintet is favorable in which each of the two Fe atoms has two unpaired electrons, and the states with the higher multiplicities 7 and 9 are only 0.10–0.15 eV higher. The calculated energies of dissociation D of the dimers into monomers point to a rather high stability of the (heme) ₂ ⁺ (D ∼ 1.4 1.4eV) and to a low stability of the neutral dimer (heme)₂ (D ∼ 0.3 eV). The R(Fe⋯O_b) distances in the bridges in (heme) ₂ ⁺ are 0.2–0.4 ? shorter than in (heme)₂. The trends in the behavior of the energetic and structural characteristics of the dimers (R(Fe-N), displacements of Fe atoms from the porphyrin ring plane, character of ring distortions, etc.) associated with the involvement of the and AOs of Fe atoms in bonding, as well as the spin density distribution over the Fe atoms and the rings, are analyzed as a function of the multiplicity and charge of the system. Differences in the character of interaction of the heme and ferriporphyrin dimers with molecular oxygen are discussed. Original Russian Text ? O.P. Charkin, N.M. Klimenko, D.O. Charkin, S.H. Lin, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 7, pp. 1166–1174.     

Single vibronic level photochemistry of NO2 in the 2491 Å system

A photochemical decomposition study of NO₂(B?²B₂) in specified vibronic states is reported. The O(¹D)-atom yields below and above the dissociation limit (40973 cm^?1) have been measured. The role played by the rotational excitation energy and the vibrational excitation modes in promoting the predissociation is discussed.     

Mg(BO2)2在MgCl2水溶液中的相平衡与化学平衡

借助拉曼光谱和X射线衍射(XRD)检测手段,对Mg(BO_2)_2在MgCl_2水溶液中水解的固液相平衡与物种化学平衡规律进行了研究。结果表明,MgCl_2对Mg(BO_2)_2的溶解转化、多硼氧配阴离子的物种分布有很大影响:(1)随着MgCl_2浓度从0达到饱和,Mg(BO_2)_2的表观饱和浓度从0.79%增加到1.96%,pH值从9.96降到6.27;(2)Mg(BO_2)_2在纯水中水解形成固相Mg_2B_6O_(11)·15H_2O和Mg(OH)_2,在MgCl_2溶液中形成固相Mg_2B_6O_(11)·15H_2O和Mg_3Cl_2(OH)_4·4H_2O;(3)Mg(BO_2)_2在纯水中水解,硼的物种主要为B_4O_5(OH)_4~(2-)和B_3O_3(OH)_4~-,分别占液相总硼含量的49.81%和19.54%。在MgCl_2饱和溶液中,主要为B_3O_3(OH)_4~-和B_5O_6OH)_4~-,分别占液相总硼含量的44.57%和40.00%。     

The energy balance and branching ratios associated with the chemiluminescent reaction Si(3P) + N2O(1Σ) → SiO*(a3Σ+, b3Π, A1Π) + N2(υ″ ⩾ 5) — possible formation of vibrationally excited N2

Silicon atoms react under single collision conditions with N₂O to yield chemiluminescent emission corresponding to the SiO a³Σ⁺?X¹Σ⁺ and b³Π?X¹Σ⁺ intercombination systems and the A¹Π?X¹Σ⁺ band system. A most striking feature of the SiN₂O reaction is the energy balance associated with the formation of SiO product molecules in the A¹Π and b³Π states. A significant energy discrepancy ( = 10000 cm^? = 1.24 eV) is found between the available energy to populate the highest energetically accessible excited-state quantum levels and the highest quantum level from which emission is observed. It is suggested that this discrepancy may result from the formation of vibrationally excited N₂ in a concerted fast SiN₂O reactive encounter. Emission from the SiO a³Σ⁺ (A¹Π) and b³Π(A¹Π, E¹Σ₀⁺) triplet-state manifold results primarily from intensity borrowing involving the indicated singlet states. Perturbation calculations indicate the magnitude of the mixing between the b³Π, A¹Π and E¹Σ₀⁺ states ranges between 0.5 and 2%. On the basis of these calculations, the branching ratio (excited triplet)/(excited singlet) is found to be well in excess of 500. An approximate vibrational population distribution is deduced for those molecules formed in the b³Π state. The present studies are correlated with those of previous workers in order to provide an explanation for diverse relaxation effects as well as observed changes in the ratio of a³Σ⁺ to b³Π emission as a function of pressure and experimental environment. Some of these effects are attributable to a strong coupling between the a³Σ⁺ and b³Π state. Based on the current results, there appears to be little correlation between either (1) the branching ratio for excited state formation or (2) the total absolute cross section for excited-state formation and (3) the measured quantum yield for the SiN₂O reaction. Implications for chemical laser development are considered.