Breakdown of the spectator model for the OH bonds in studying the H+H2O reaction

The time-dependent wave packet method is used to study the exchange and abstraction processes for the H+H2O reaction with both OH bonds in the H2O reactant treated as reactive bonds in full dimension. The calculation clearly shows that it is necessary to treat both OH bonds in this way in order to accurately investigate the exchange process. However, for the abstraction process, the spectator model works very well. Nonreactive treatment of one OH bond by using a few vibrational basis functions or even freezing the bond can yield very accurate abstraction reaction probability.     

Theoretical study of stereodynamics for the O（3P） ＋ H2 → OH ＋ H reaction

This paper employs the quasi-classical trajectory calculations to study the influence of collision energy on the title reaction on the potential energy surface of the ground ³A' triplet state developed by Rogers et al. (J. Phys. Chem. A 2000 104 2308). It calculates the product angular distribution of P(θ_r), P(φ_r) and P(θ_r, φ_r) which reflects vector correlation. The distribution P(θ_r) shows that product rotational angular momentum vectors j' of the products are strongly aligned along the relative velocity direction k. The distribution of P(φ_r) implies a preference for left-handed product rotation in planes parallel to the scattering plane. Four different polarisation-dependent cross-sections are also presented in the centre-of-mass frame. Results indicate that OH is sensitively affected by collision energies of H₂.     

Insertion and abstraction pathways in the reaction O(1D2) + H2-->OH+H

Rigorous quantum dynamical calculations have been performed on the ground 1 1A' and first excited 1 1A" electronic states of the title reaction, employing the most accurate potential energy surfaces available. Product rovibrational quantum state populations and rotational angular momentum alignment parameters are reported, and are compared with new experimental, and quasiclassical trajectory calculated results. The quantum calculations agree quantitatively with experiment, and reveal unequivocally that the 1 1A" excited state participates in the reaction.     

Determination of the activation energy for OH desorption in the H2 + O2 reaction on Polycrystalline Platinum

We have investigated the temperature dependence of the desorption rate of OH produced in the oxidation of hydrogen on polycrystalline Pt by using laser induced fluorescence (LIF). Arrhenius type plots of OH desorption rates give quite straight lines, with an “apparent” desorption energy, E^a_OH, in the rang 1.4–2.3 eV depending on the relative hydrogen concentration. E^a_OH, differs from the “true” desorption energy, E^d_OH, due to the temperature dependence of the surface coverage of θ_OH,. Knowing θ_OH, from kinetic modelling calculation of this reaction we deduce E^d_OH, to be 2.0 ± 0.15 eV.     

Effect of a single quantum rotational excitation on state-to-state dynamics of the O(1D)+H2-->OH+H reaction

Crossed molecular beams scattering experiments on the O(1D)+H2 reaction have been carried out in order to study the effect of the reagent (H2) rotational excitation on the detailed dynamics of this benchmark insertion reation. Experimental results indicate that a single quantum rotational excitation of H2 has a significant impact on the product state distributions at the forward and backward scattering directions, while very little effect has been found in the sideway scattering direction. No clear patterns of this effect are found in the OH-product state distributions, indicating that the single quantum excitation on the dynamics is rather complicated.     

Cross section for the H+H2O abstraction reaction: experiment and theory

The absolute value of the cross section for the abstraction reaction between fast H atoms and H2O has been determined experimentally at a mean collision energy of 2.46 eV. The OH population distribution at the same mean energy has also been determined. The new measurements are compared with state-of-the-art quantum mechanical and quasiclassical scattering calculations on the most recently developed potential energy surface.     

Kinematics of the reaction H2O+(H2,H)H3O+

The kinematics of the reaction H₂O⁺(H₂,H)H₃O⁺ were studied in crossed-beam experiments in the low collision-energy range 0.1–2 eV (c.m.). The scattering diagrams, center-of-mass angular distributions, and product relative translational energy distributions obtained show that the reaction proceeds predominantly by the impulsive, stripping mechanism. The translational exoergicity vs. collision energy plot obeys the spectator-stripping prediction.     

State to state to state dynamics of the D+H2 -->HD+H reaction: control of transition-state pathways via reagent orientation

The influence of reagent rotation on the dynamics of the D+H2 -->HD+H reaction is studied. The state-resolved differential cross section is measured using the Rydberg-atom scheme in a crossed beam experiment. It is found that the H2 rotation has a strong influence on the results. This effect was traced to the selection of the quantum bottleneck states through reagent orientation, thus suggesting a novel strategy to control the transition-state pathways in direct chemical reactions.     

Simultaneous single-shot imaging of OH and O2 using a two-wavelength excimer laser

A technique is described for simultaneous single-shot imaging of OH and O₂. Laser-induced fluorescence of both molecules is excited by a tunable KrF laser, which is operated simultaneously on two wavelengths. By using two CCD detectors with image intensifiers and suitable filters, separate images of OH and O₂ distributions in H₂/O₂ and hydrocarbon/air flames were obtained.     

Theoretical study on collision dynamics of H+ + H2O at low energies

Scattering dynamics of a water molecule in collision with proton is studied based on a time-dependent density functional theory and coupled with the molecular dynamics method, in which the electrons are described by quantum mechanics and the nuclei are described by classical mechanics. Four different incident directions at 46 eV are chosen in order to investigate the orientations effect, and the energy-dependent effect in low energy region is explored under impact energies 27, 36 and 46 eV. Reaction channels, scattering angles and energy loss of protons are calculated. The differences between those characteristics are unobvious in large impact parameters, which are irrespective of the incident orientations due to weak projectile-target interaction. In small impact parameters, the results strongly depend on the collision energy and orientation.     

Rotational distribution of nascent OH radicals after H2O2 photolysis at 193 nm

The rotational distribution of OH(X ²,v=0) radicals was investigated by resonant laser-induced fluorescence (LIF) after photolysis of H₂O₂ at 193 nm. A microcomputer equipped LIF arrangement allowed special shot-by-shot normalization of the fluorescence signal for noise reduction. Using a least-squares procedure we were able to account for all measured line intensities including overlapping lines (blends) and obtain a complete rotational state distribution of the OH(X ²,v=0) state. The rotational excitation shows a Gaussian-like distribution with a maximum atK=12 and with 16% of the total available energy (17,400 cm^–1) appearing in rotation. Only 1% of the available energy is converted into vibration, leaving over 83% for translational excitation. The measured rotational distribution appears to fit a semiclassical theory.     

Efficiencies of third bodies in the reaction H + O2 + M = HO2 + M

Vibrational transition probabilities have been calculated by the Schwartz, Slawsky and Herzfeld method [3] for the deactivation of HO₂* in collision with H₂, O₂ and CO₂. The relative efficiencies of H₂, O₂ and CO₂ are compared with their third-body efficiencies found experimentally and it is concluded that the transfer of large vibrational quanta from HO₂* is unlikely to play an important part in determining the position of the second explosion limit of the H₂/O₂ reaction. This conclusion is at variance with the explanation put forward by Walsh [1] of the ‘anomalous’ third-body efficiencies of H₂O and CO₂ in this reaction.     

Two-photon predissociative fluorescence of H2O by a KrF laser for concentration and temperature measurement in flames

Two-photon laser-induced predissociative fluorescence (LIPF) of H₂O is examined as a potential measurement technique of H₂O concentration and temperature in flames. Two-photons of 248 nm light from a narrowband KrF laser excite H₂O to the highly predissociative state in a hydrogen-air flame. The subsequent bound-free emission is observed from 400–500 nm in the flame at temperatures of 1000–2000 K and is found to be free of fluorescence interference from other flame species. This LIPF signal is not affected by collisional quenching due to the short lifetime of the predissociative state (2.5 ps). Broadband laser dispersion spectra, narrowband laser dispersion spectra, laser excitation spectra and probability density functions of the H₂O fluorescence are obtained in the hydrogen flame. The H₂O LIPF signal is found to be temperature sensitive and a two-line LIPF technique is needed for concentration and temperature measurement. The accuracy of a two-line LIPF technique for H₂O concentration and temperature measurement is determined.     

气相中2Sr+,2Ba+介入N2O与H2反应的理论研究

运用密度泛函理论DFT-UB3LYP方法,对2Sr+、2Ba+采用相对论校正赝势基组SDD,对N、O、H采用6-311+G(2d,p)基组,计算研究了气相中碱土金属离子2Sr+、2Ba+介入N2O(1∑+)和H2(1∑g+)反应的微观机理,优化了二重态势能面上各反应物、中间体和过渡态的构型特征,用频率分析方法和内禀反应坐标方法(IRC)对过渡态进行了验证.运用Kozuch撰写的能量跨度模型(Energetic Span Model,δlE),确定了决定循环反应速率的决速过渡态(TDTS)和决速中间体(TDI),并利用转化频率(Turnover Frequency,TOF)评估了催化性能.结果表明:从热力学性质分析2Sr+、2Ba+离子对N2O(1∑+)和H2(1∑+g)反应很好的催化作用,可得到目标产物N2(1∑g+)和H2O(1 A1),却从动力学性质分析主要反应产物为N2、SrOH+ (BaOH+)和H,最终动力学因素在反应中起决定性作用,以上结论与实验观测结果相符.     

Development of the reaction time accelerating molecular dynamics method for simulation of chemical reaction

We present a novel and efficient method to integrate chemical reactions into molecular dynamics to simulate chemical reaction systems. We have dubbed this method RTAMD, an acronym for reaction time accelerating molecular dynamics. The methodology we propose here requires no more than the knowledge of the empirical intermolecular potentials for the species at play as well as the elementary reaction path among them. Bond formation during the simulation is performed by changing the inter-atomic potentials from those of the non-bonded species to those of the bonded ones, and a reaction is deemed to occur by the distance separating the bond forming atoms. In this way the energy barrier for a reaction is no longer considered; the estimation of the reaction rate, however, is possible by introducing the principles of the transition state theory. The simplicity of the present scheme to simulate chemical reactions enables it to be used in large-scale MD simulations involving a large number of simultaneous chemical reactions and to evaluate kinetic parameters. In this paper, the basic theory of the method is presented and application to simple equiatomic reaction system where the reaction rates were estimated was illustrated.