Penning ionization of NO and O2(1Δg) by argon in the 3P1 state

Electronically excited argon in the ³ P ₁ state was generated in a flow system by resonance absorption of the λ=106·7 nm emission line. This photochemical source is particularly convenient for kinetic studies since Ar(³ P ₁) alone is produced in the primary exciting step. Energy transfer from excited argon may lead to Penning ionization:

This process has been studied for M=NO and M=O₂(¹Δ _g ). Relative concentrations of Ar* were estimated from the Penning ion current, and it is shown that Ar* is probably in the initially excited ³ P ₁ state and not in the metastable ³ P ₂ state. Kinetic studies showed that Penning ionization of NO occurs for about one in every five gas kinetic collisions with Ar(³ P ₁). The Penning process can only compete effectively with radiative loss of Ar(³ P ₁) as a result of extensive imprisonment of resonance fluorescence. Penning ionization of O₂(¹Δ _g ) is shown to proceed at nearly the same rate as ionization of NO. The decrease in Penning ion current on addition of a quenching gas, such as N₂ or O₂, is used to derive rate constants for the quenching process relative to the rate of quenching by NO. Estimated absolute rate constants are presented in a table.     

Observation of a strong correlation between g(2+ γvib) and g(2+ rot) in strongly deformed nuclei

The E2/M1 multipole mixing parameters of cascade transitions in γ-vibrational bands of ¹⁵⁴Gd, ¹⁶⁶Er and ¹⁶⁸Er have been determined by γ -@#@ γ directional correlation measurements as: \(\delta \left( {{}^{154}{\text{Gd}}\left( {3_\gamma ^ + \to 2_\gamma ^ + } \right)} \right) = - 4.3_{ - 2.1}^{ + 9.4}\) and \(\delta \left( {{}^{166}{\text{Er}}\left( {5_\gamma ^ + \to 4_\gamma ^ + } \right)} \right) = + 1.94_{ - 0.21}^{ + 0.23}\) (with conversion data [15] taken into account) These data were used to derive g(2⁺γvib) ? g(2⁺ rot). The results, together with g-factors derived from direct measurements by IPAC and Mossbuer spectroscopy [10] or by use of transient fields [9, 31] exhibit a strong correlation between both g-factors, i.e. if g(2⁺ rot) is large g(2⁺ γvib) is small and vice versa. The most direct and most simple interpretation is the assumption of a more or less different density distribution of protons and neutrons in the nuclei.     

Vibrational population of the O2(b1Σ g + ) state in a low-Pressure oxygen pulsed discharge

The study of the vibrational state population of the O₂(b¹ _g ⁺ ) metastable state in a pure oxygen DC pulsed discharge is presented. The vibrational temperature is evaluated from the relative populations of v = 0, 1 and 2 states. The populations are determined from the intensities of (0-0), (1-1), (1-0) and (2-1) transitions of the atmospheric system. The most intensive (0-0) and (1-1) bands are used in the time-resolved measurements in order to determine the time evolution of the vibrational temperature during the discharge pulse.     

An insight into the reaction kinetics of CH3 + O2(a1Δg) and its enhancement effect on methane ignition

The reaction between CH₃ and O₂(a¹?_g) is crucial to understand the effects of electronically excited oxygen in plasma-assisted combustion of methane and other hydrocarbons. In the present work, multireference quantum chemical methods were used to investigate the potential energy surface of CH₃ + O₂(a¹?_g). The RRKM/master equation simulation was employed to compute the rate coefficients of various pathways to this reaction over the temperature range of 300–2000 K and a pressure range of 0.1–100 atm. Special attention has been paid to the nonadiabatic transition between the excited state and ground state, which directly leads to a quenching channel from CH₃ + O₂(a¹?_g) to CH₃ + O₂(X³∑_g^?). This quenching reaction has been overlooked by previous theoretical and kinetic modeling studies. We also conducted kinetic modeling to examine the effect of this reaction on the ignition enhancement of methane oxidation. Although the channel of CH₃ + O₂(a¹?_g) quenching to CH₃ + O₂(X³∑_g^?) has nonnegligible rate constants comparing with other reaction channels, modeling result with the inclusion of 5% O₂(a¹?_g) in molecular oxygen shows that the titled reactions shorten the ignition delay time of methane by more than twenty times at 900 K, 1 atm. The ignition enhancement is mainly from the chain branching channels to CH₂O + OH and CH₃O + O which has been greatly promoted by excess energy from O₂(a¹?_g). The present study uncovers the kinetic mechanism of this nonadiabatic reaction and provides reasonable rate coefficients for further kinetic modeling of plasma-assisted combustion of methane and other hydrocarbons.     

Theoretical study of the O(1D) + H2(1Σ g +) reactive quenching process

Classical trajectory calculations have been made for the system O(¹ D) + H ₂(¹Σ _g ⁺) →OH(²Π) + H(² S) using an analytical singlet ground state surface for H ₂O. A rate constant of 1·73 × 10^-10 cm³ molecule^-1s^-1 at 300 K has been obtained. The distribution of energy in the products is approximately 30 per cent in translation, 45 per cent in vibration and 25 per cent in rotation. Because of the preponderance of vibrationally long-lived trajectories, statistical theories gave a good interpretation of the gross features of the reaction.     

μSR study of a mixed compound NiC2O4 2⋅(2-methylimidazole)x(H2O)1-x

We examined the muon spin relaxation (μSR) of mixed compounds NiC₂O₄ 2⋅(2-methylimidazole)_x(H₂O)_1-x with x=1.0 and 0.49. Although the macroscopic magnetic properties are obviously different from each other, both systems exhibit similar behavior in the muon spin relaxation. In addition, in the x=0.49 (SG) sample, a critical slowing down of spin dynamics was not observed in this μSR measurement, though the spin-glass like freezing was observed in the susceptibility measurements. Qualitative explanation of these anomalous observations is given. This revised version was published online in August 2006 with corrections to the Cover Date.     

The quenching of excited F(2 P 1/2) and Cl(2 P 1/2) atoms by N2(X 1Σ g + ) molecules

The rate constant for the quenching of excited F(² P _1/2) and Cl(² P _1/2) atoms in collisions with N₂ molecules were calculated. The electron interaction matrix between N₂(X ¹Σ _g ⁺ ) and F and Cl atoms in the ² P _j state calculated asymptotically taking into account quadrupole-quadrupole, dispersion, and exchange interactions was used. The dynamic problem of electronic transitions was solved using the modified wave number approximation, the exactly solvable semiclassical exponential nonadiabatic bond model, and the method of phase functions.     

Study of collisional deactivation of O2(b 1Σ g + ) molecules in a hydrogen-oxygen mixture at high temperatures using laser-induced gratings

Collisional deactivation of O₂(b ¹Σ _g ⁺ ) molecules resonantly excited by a 10 ns pulse of laser radiation with a wavelength of 762 nm in H₂/O₂ mixtures is experimentally studied. The radiation intensity and hence the molecule excitation efficiency have a spatially periodic modulation that leads to the formation of laser-induced gratings (LIGs) of the refractive index. The study of LIG temporal evolution allows collisional relaxation rates of molecular excited states and gas temperature to be determined. In this work, the b ¹Σ _g ⁺ state of O₂ molecules deactivation rates are measured in a 4.3 vol % H₂ mixture at the number density of 2 amg in the temperature range 291–850 K. The physical deactivation is shown to dominate in the collisions of H₂ with O₂(b ¹Σ _g ⁺ ) and O₂(a ¹Δ _g ) up to temperatures of 780–790 K at time delays up to 10 μs after the excitation pulse. The parameters of the obtained temperature dependence of the (b ¹Σ _g ⁺ state deactivation rate agree well with the data of independent measurements performed earlier at lower temperatures (200–400 K). Tunable diode laser absorption spectroscopy is used to measure the temperature dependence of the number density of the H₂O molecules which appear as the mixture, as the result of the dark gross reaction with O₂ molecules in the ground state, O₂ + 2H₂ → 2H₂O. The measurements show that this reaction results in complete transformation of H₂ into H₂O at temperatures of 790–810 K.     

O2分子激发态a1△g和b1∑+g态的分析势能函数

以aug-co-pVQZ,cc-pV5Z,6-311++g(d,p)和6-311++g(3df,3pd)等为基函数,采用多组态相互作用(MRCI)方法对O2分子最低的两个激发态1△g和1∑+g的平衡结构、谐振频率和势能曲线进行了计算.并选用MurrelI-Sorbie势能函数对曲线进行拟合,利用拟合的参数值计算出了力常数和光谱数据.结果表明计算值与实验值符合较好.     

Time-dependent quantum wave packet and quasiclassical trajectory studies of the Au(2S) + H2(X1∑+g) → AuH(X1∑+g) + H(2S) reaction

The time-dependent quantum wave packet (TDWP) and quasiclassical trajectory calculations (QCT) are carried out for the Au(²S) + H₂(X¹∑⁺_g) → AuH(X¹∑⁺_g) + H(²S) reaction on a global potential energy surface. The reaction probabilities at a series of J values, integral cross sections (ICSs) and differential cross sections of the title reaction are calculated by the TDWP method. For reaction probabilities, there are a mass of sharp oscillations at low collision energy, which can be attributed to resonances supported by the potential well. Due to the endothermicity of the title reaction, the total ICS shows a threshold about 1.53 eV. In order to further investigate the reactive mechanism, the lifetime of complex is calculated by QCT method. At the low collision energy, most intermediate complexes are long lived, which implies that the reaction is governed by indirect reactive mechanism. With the collision energy increasing, the direct reactive mechanism occupies the dominant position. Due to the change of the reactive mechanism, the angular distribution shifts toward the forward direction with collision energy increasing. The isotopic variant, Au + D₂→AuD + D reaction, is also calculated by TDWP method. The calculated reaction probabilities and ICSs show that the isotope effect reduces the reactivity.     

Synthesis and characterization of magnetic diphase ZnFe(2)O(4) /γ-Fe(2)O(3) electrospun fibers

Magnetic nanofibers of ZnFe₂O₄/γ-Fe₂O₃ composite were synthesized by electrospinning from a sol-gel solution containing a molar ratio (Fe/Zn) of 3. The effects of the calcination temperature on phase composition, particle size and magnetic properties have been investigated. Zinc ferrite fibers were obtained by calcinating the electrospun fibers in air from 300 to 800 °C and characterized by thermogravimetric analyses, Fourier transformed infrared spectroscopy, X-ray photoemission spectroscopy, X-ray diffraction, vibration sample magnetometry and magnetic force microscopy. The resulting fibers, with diameters ranging from 90 to 150 nm, were ferrimagnetic with high saturation magnetization as compared to bulk. An increase in the calcination temperature resulted in an increase in particle size and saturation magnetization. The observed increase in saturation magnetization was most likely due to the formation and growth of ZnFe₂O₄/γ-Fe₂O₃ diphase crystals. The highest saturation magnetization (45 emu/g) was obtained for fibers calcined at 800 °C.     

Identification of a 3+ state in16O and evidence for a (1f 7/2 1p 1 2/−1 ) component in its wave function

Excitation functions and angular distributions for the elastic scattering of protons on¹⁵N and the reactions¹⁵N(p, α ₀)¹²C and¹⁵N(p,α ₁)¹²C^* were measured in the proton energy range of 2.50?5.14 MeV (E _x (¹⁶O)=14.47?16.94 MeV). Besides known resonances two new ones were found at 16.46 and 16.82MeV. For the latterJ ^?=3⁺ is assigned using the compound nucleus theory. The wave function of this state contains a (1f _7/2 1p ₁ ^2/?1 )₃-particle-hole-component. Earlier spin parity assignments of other resonances are discussed.     

Lifetimes of rovibrational levels of the long-range I′ 1Πg state of H2 and D2: experiment and theory

The lifetimes of the lowest lying rovibrational levels of the outer well I′ ¹Π_g state of molecular hydrogen were measured for both H₂ and D₂. The measurements were made by direct observation of the time-dependent decay of the fluorescence. The observed lifetimes depend on isotopomer and increase with vibrational excitation. The predominant decay route for these levels is fluorescence. Previously published ab initio lifetimes calculated for these states, which accounted for non-adiabatic interactions [J. Chem. Phys. 92, 7461 (1990)], are in good agreement with experiment for H₂ but are too long by four or five orders of magnitude for D₂. We present new ab initio results at the adiabatic level for the fluorescence lifetimes. The current results are in reasonable agreement with the experimental lifetimes for both H₂ and D₂. We explain the isotopomer and vibrational dependence of the lifetimes and discuss the neglected interactions and decay pathways.     

CH4+O2体系中碰撞-诱导O2(X3∑-g→a1Δg)跃迁几率计算

采用从头计算二阶自旋-轨道多组态准简并微扰理论计算了CH4+O2体系中O2分子X3∑-g-a1Δg,X3∑-g-b1∑+g和b1∑+g-a1Δg的碰撞-诱导跃迁几率,分析了O2分子振动对跃迁几率的影响,并与O2+H2模型的结果做了比较.     

High-Resolution Spectroscopy of Jet-Cooled (32)SO(2) and (34)SO(2): The ã(3)B(1)-;X(1)A(1), 2(1)(0) and 1(1)(0) Bands

Laser-induced excitation spectra of the two bands ?(3)B(1)-;X(1)A(1), 2(1)(0) and 1(1)(0) of (32)SO(2) and (34)SO(2) have been recorded in a supersonic jet at a resolution of 0.015 cm(-1). The rotational and electron-spin fine structure has been analyzed for both isotopic species. Analysis of the rotational and electron-spin fine structure yields precise values of the rotational constants A, B, and C and the spin constants alpha and beta for both (32)SO(2) and (34)SO(2) in the states ?(3)B(1) (010) and (100). No interaction between these two vibrational states with any nearby triplet state is observed for rotational levels with J 相似文献   

Analysis of the interactions in FCCF:(H2O) and FCCF:(H2O)2 complexes through the study of their indirect spin–spin coupling constants

A theoretical study of FCCF:(H₂O)_n complexes, with n?=?1 and 2, has been carried out by means of ab initio computational methods. Three kinds of interactions are observed in the complexes: H···π and H···F hydrogen bonds and O···FC tetrel bonds. The indirect spin–spin coupling constants have been calculated at the CCSD/aug-cc-pVTZ-J computational level. Special attention has been paid to the dependence of the different intramolecular coupling constants in FCCF on the distance between the coupled nuclei and the presence or absence of water molecules. The exceptional sensitivity shown by these coupling constants to the presence of water molecules is quite notorious and can provide information on the bonding structure of the molecule.     

Adsorption and diffusion of an Au atom and dimer on a θ-Al2O3 (001) surface

With density-functional calculations we have investigated adsorption and diffusion of an Au atom and an Au₂ dimer on a θ-Al₂O₃(001) surface. The surface structure of θ-Al₂O₃(001) has an armchair-like configuration containing flat and trench areas and the Au_n (n = 1 or 2) cluster prefers to adsorb on the flat area. A single Au atom adsorbs on an O–Al bridge site with adsorption energy 0.35 eV, whereas an Au₂ dimer bonds to the oxide with adsorption energy 0.78 eV, with one Au coordinated singly to a surface O. Formation of Au₂ from Au₁ is favored, with a negligible energy barrier. The calculated energy barriers for diffusion indicate that an Au atom diffuses more rapidly than an Au₂ dimer but both prefer to diffuse anisotropically, along the flat area of the θ-Al₂O₃(001) surface.     

Quantum and quasiclassical dynamics of C(3P)+H2(1∑+g)→ H(2S)+CH(2Π)reaction:Coriolis coupling effects and stereodynamics

The dynamics of C+H2 → H+CH reaction is theoretically studied using the quasiclassical trajectory and quantum mechanical wave packet methods.The analysis of rea...     

Crystal structure of the inverse weberite ZnFeF5(H2O)2, magnetic and mössbauer study of the antiferromagnet ZnFeF5(H2O)2 and ferrimagnet Mn FeF5(H2O)2

The room temperature crystal structure of the inverse weberite ZnFeF₅ (H₂O)₂ is refined from powder X-ray diffraction. The cell is orthorhombic (S.G. Imma, a = 7.475(1) →A, b = 10.766(1) →A, c = 6.594(1) →A, z = 4). Below T_N = 9(2) K, ZnFeF₅(H₂O)₂ becomes a 1-D antiferromagnet. This behaviour was characterized by susceptibility and magnetization measurements and Mössbauer spectroscopy. On the contrary, isotypic MnFeF₅(H₂O)₂ is confrimed to be a ferrimagnet below T_c = 39.5(1)K. Its magnetic and Mössbauer characteristics are, above and below T_c,and agree with a 3-D magnetic character. Ferrimagnetism could be due to frustration effects as in previously described Fe₂F₅(H₂O)₂.