H+HF(v,j)→H+HF(v′,j′)的传能动力学理论研究

本文运用非含时量子动力学方法研究了H+HF(v=1,j)→H+HF(v'=0,j')传能过程在295~500 K的振动弛豫速率常数.在此温度范围内,所有转动分辨的振动弛豫速率常数随着温度升高而单调递增,速率常数最大的末态转动量子数随着初态转动量子数的增加而增加.在室温下,振动态分辨的振动弛豫速率常数与实验值符合较好.同时,我们也计算了H+HF(v=1,j)→H+HF(v'=1,j')纯转动传能过程在500 K的速率常数,发现它们整体上比振动弛豫速率常数大了几个数量级,并且△j=-1的速率常数一般大于△j=-1的速率常数.     

The polarization dependent differential cross sections of the reactions:H+LiH~+(v=0,j=0)→H_2+Li~+ and H~++ LiH(v=0,j=0)→H_2~++Li

<正>Quasi-classical trajectory(QCT) calculations have been carried out to study the generalized polarization dependent differentialcross sections(PDDCSs) for the reactions H + LiH~+(v = 0,j = 0)→H_2 + Li~+ and H~+ + LiH(v = 0,j = 0)→H_2~+ + Li occurring onthe two lowest-lying electronic states of the LiH_2~+ system,using the ab initio potential energy surfaces(PESs) of Martinazzo et al.[3].Four PDDCSs,i.e.,(2π/σ)(dσ_(00)/dω_t),(2π/σ)(dσ_(20)/dω_t),(2π/σ)(dσ_(22+)/dω_t),(2π/σ)(dσ_(21-)/dω_t) have been discussed in detail.     

准经典轨线研究Li+HF(v=0,j=O)→LiF+H反应动力学

基于Aguado等人拟合的APW势能面(PES),运用准经典轨线(QCT)方法,对反应Li+HF(v=0,j=0)→LiF+H的动力学性质进行了计算.主要研究了不同碰撞能条件下的反应截面、转动取向、产物散射角分布和竞争反应模式等.结果表明,该反应存在直接提取型和间接插入型两种反应模式,在低能量下反应以间接插入反应模式为主,能量大于200 meV时则以直接提取反应为主.     

Depolarization of rotational angular momentum in CN(A2Π, v = 4) + Ar collisions

Angular momentum depolarization and population transfer in CN(A(2)Π, v = 4, j, F(1)e) + Ar collisions have been investigated both experimentally and theoretically. Ground-state CN(X(2)Σ(+)) molecules were generated by pulsed 266-nm laser photolysis of ICN in a thermal (nominally 298 K) bath of the Ar collision partner at a range of pressures. The translationally thermalized CN(X) radicals were optically pumped to selected unique CN(A(2)Π, v = 4, j = 2.5, 3.5, 6.5, 11.5, 13.5, and 18.5, F(1)e) levels on the A-X (4,0) band by a pulsed tunable dye laser. The prepared level was monitored in a collinear geometry by cw frequency-modulated (FM) spectroscopy in stimulated emission on the CN(A-X) (4,2) band. The FM lineshapes for co- and counter-rotating circular pump and probe polarizations were analyzed to extract the time dependence of the population and (to a good approximation) orientation (tensor rank K = 1 polarization). The corresponding parallel and perpendicular linear polarizations yielded population and alignment (K = 2). The combined population and polarization measurements at each Ar pressure were fitted to a 3-level kinetic model, the minimum complexity necessary to reproduce the qualitative features of the data. Rate constants were extracted for the total loss of population and of elastic depolarization of ranks K = 1 and 2. Elastic depolarization is concluded to be a relatively minor process in this system. Complementary full quantum scattering (QS) calculations were carried out on the best previous and a new set of ab initio potential energy surfaces for CN(A)-Ar. Collision-energy-dependent elastic tensor and depolarization cross sections for ranks K = 1 and 2 were computed for CN(A(2)Π, v = 4, j = 1.5-10.5, F(1)e) rotational/fine-structure levels. In addition, integral cross sections for rotationally inelastic transitions out of these levels were computed and summed to yield total population transfer cross sections. These quantities were integrated over a thermal collision-energy distribution to yield the corresponding rate constants. A complete master-equation simulation using the QS results for the selected initial level j = 6.5 gave close, but not perfect, agreement with the near-exponential experimental population decays, and successfully reproduced the observed multimodal character of the polarization decays. On average, the QS population removal rate constants were consistently 10%-15% higher than those derived from the 3-level fit to the experimental data. The QS and experimental depolarization rate constants agree within the experimental uncertainties at low j, but the QS predictions decline more rapidly with j than the observations. In addition to providing a sensitive test of the achievable level of agreement between state-of-the art experiment and theory, these results highlight the importance of multiple collisions in contributing to phenomenological depolarization using any method sensitive to both polarized and unpolarized molecules in the observed level.     

Computation of cross sections for the F+H2(v=0,j=0) → FH(v′j)+H reaction by the hyperspherical method

Summary A quantum mechanical calculation of cross sections for the reaction F+H₂(v=0,j=0) FH(vj)+H has been performed on the T5A semiempirical potential surface using hyperspherical coordinates. State-to-state integral and differential cross sections converge rapidly with the number of components of the total angular momentum projection onto the axis of least inertia. Thev=3 differential cross section has a forward peak whose magnitude increases with energy whereas thev=2 differential cross section has a backward maximum, in qualitative agreement with cross-beam experiments. Thev=2 andv=3 rotational distributions are in rather good agreement with experiment, but not the vibrational branching ratios.     

Semiclassical glory analyses in the time domain for the H + D2(v(i) = 0, j(i) = 0) → HD(v(f) = 3, j(f) = 0) + D reaction

We make the first application of semiclassical (SC) techniques to the plane-wavepacket formulation of time-domain (T-domain) scattering. The angular scattering of the state-to-state reaction, H + D(2)(v(i) = 0, j(i) = 0) → HD(v(f) = 3, j(f) = 0) + D, is analysed, where v and j are vibrational and rotational quantum numbers, respectively. It is proved that the forward-angle scattering in the T-domain, which arises from a delayed mechanism, is an example of a glory. The SC techniques used in the T-domain are: An integral transitional approximation, a semiclassical transitional approximation, a uniform semiclassical approximation (USA), a primitive semiclassical approximation and a classical semiclassical approximation. Nearside-farside (NF) scattering theory is also employed, both partial wave and SC, since a NF analysis provides valuable insights into oscillatory structures present in the full scattering pattern. In addition, we incorporate techniques into the SC theory called "one linear fit" and "two linear fits", which allow the derivative of the quantum deflection function, Θ?(')(J), to be estimated when Θ?J exhibits undulations as a function of J, the total angular momentum variable. The input to our SC analyses is numerical scattering (S) matrix data, calculated from accurate quantum collisional calculations for the Boothroyd-Keogh-Martin-Peterson potential energy surface No. 2, in the energy domain (E-domain), from which accurate S matrix elements in the T-domain are generated. In the E-domain, we introduce a new technique, called "T-to-E domain SC analysis." It half-Fourier transforms the E-domain accurate quantum scattering amplitude to the T-domain, where we carry out a SC analysis; this is followed by an inverse half-Fourier transform of the T-domain SC scattering amplitude back to the E-domain. We demonstrate that T-to-E USA differential cross sections (DCSs) agree well with exact quantum DCSs at forward angles, for energies where a direct USA analysis in the E-domain fails.     

H+O2(n0, j0)→HO+O及C+H2(n0, j0)→CH+H体系选态反应截面的过渡态理论计算

本文用微正则过渡态理论计算了H+O_2(n_0,j_0)→HO+O和C+H_2(n_0, j_0)→CH+H在ab initio势能面上的选态反应截面σ_(n_0,j_0); E.分析了势能面性质对反应截面的影响。计算结果表明, 在指定反应物分子的振动态n_0、转动态j_0时, 两个反应体系的反应截面随相对平动能的增加先是增加后是减小(j_0=1, n_0=0除外); 在给定相对平动能和反应物分子的转动态j_0时, 随反应物分子的振动量子数n_0的增加, 两个体系的选态反应截面均有较显著的增加, 在指定相对平动能和反应物分子的振动态n_0时, H+O_2体系的选态反应截面随j_0的变化较为复杂, 而C+H_2体系则比较简单(j_0=1除外)。对于H+O_2反应体系, 本文得到的反应截面与实验结果及准经典轨迹理论的计算结果符合得很好。     

The reaction Ne+H 2 + (v=0, 1, 2, 3, 4)→NeH++H: 3D potential energy surface and quasiclassical trajectory calculations

A three-dimensional potential energy surface for the endoergic reaction Ne+H ₂ ⁺ →NeH⁺+H in the² A′ ground state of the system NeH ₂ ⁺ has been calculated by quantum chemical ab initio methods (CEPA approximation). The calculated points on this surface were fitted to an analytic ansatz in terms of an extended LEPS functional form augmented by a correction function. The latter was expanded in polynomials in inverse powers of the internuclear distances. This analytic form was used for quasiclassical trajectory calculations of reactive cross sections. In agreement with experimental investigations a strong vibrational enhancement is observed, i.e. the reaction is markedly favored if the necessary reaction energy is supplied as vibrational energy of H ₂ ⁺ rather than as relative translational energy. Other properties of the reaction dynamics such as the backward to forward scattering ratio, the lifetime of the collision complex NeH ₂ ⁺ , and final rotational and vibrational state distributions are also discussed on the basis of the quasiclassical trajectory calculations.     

Quasi-Classical Trajectory Study on O++DH (v=0, j=0)→OD++H Reaction at Different Collision Energy

The quasi-classical trajectory calculations O⁺+DH (v=0, j=0)→OD⁺+H reactions on the RODRIGO potential energy surface have been carried out to study the isotope effect onstereo-dynamics at the collision energies of 1.0, 1.5, 2.0, and 2.5 eV. The distributions of dihedral angle P(φr) and the distributions of P(θr) are discussed. Furthermore, the angular distributions of the product rotational vectors in the form of polar plot in θr and φr are calculated. The differential cross section shows interesting phenomenon that the reaction is dominated by the direct reaction mechanism. Reaction probability and reaction cross section are also calculated. The calculations indicate that the stereo-dynamics properties of the title reactions are sensitive to the collision energy.     

Angular scattering using parameterized S matrix elements for the H + D2(v(i) = 0, j(i) = 0) → HD(v(f) = 3, j(f) = 0) + D reaction: an example of Heisenberg's S matrix programme

A neglected topic in the theory of reactive scattering is the use of parameterized scattering (S) matrix elements to calculate differential cross sections (DCSs). We construct four simple parameterizations, whose moduli are smooth step-functions and whose phases are quadratic functions of the total angular momentum quantum number. Application is made to forward glory scattering in the DCS of the H + D(2)(v(i) = 0, j(i) = 0) → HD(v(f) = 3, j(f) = 0) + D reaction at a translational energy of 1.81 eV, where v and j are vibrational and rotational quantum numbers respectively. The parameterized S matrix elements can reproduce the forward scattering for centre-of-mass reactive scattering angles up to 30° and can identify the total angular momenta (equivalently, impact parameters) that contribute to the glory. The theoretical techniques employed to analyze structure in the DCS include: nearside-farside theory, local angular momentum theory--in both cases incorporating resummations of the partial wave series representation of the scattering amplitude--and the uniform semiclassical theory of forward glory scattering. Our approach is an example of Heisenberg's S matrix programme, in which no potential energy surface is used. Our calculations for the DCS using the four parameterized S matrix elements are counterexamples to the following universal statements often found in the chemical physics literature: "every molecular scattering investigation needs detailed information about the interaction potential," and "an accurate potential energy surface is an essential element in carrying out simulations of a chemical reaction". Both these statements are false.     

Quantum scattering LCAC-SW theory studies on reaction probabilities of three-dimensional H+H_2(υ,j)→H_2(υ′, j′)+H reaction

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Ba+HF(v,J)→BaF(v′,J′)+H反应的准经典轨线研究

首次构造了放热反应Ba+HF(v,J)→BaF(v′,J′)+H的LEPS势能面,并且进行了准经典轨线研究. 对于初始基态,和初始第一激发态的反应物HF,计算得到的BaF产物态分布与实验吻合得比较好. 对产物取向的研究表明,反应体系的质量组合是产物取向的决定因素.反应过程中,直接的提取反应和间接的插入反应是两种竞争的微观反应通道,这种竞争是由于在Ba原子进攻HF分子的时候,即使进攻方向偏离了HF共线的方向也不会引起能垒高度的明显增加.而且低的反应物平动能倾向于提取反应而高的HF振动激发会导致插入反应.     

准经典轨线研究Li+HF(ν=0, j=0)→LiF+H反应动力学

基于Aguado等人拟合的APW势能面(PES), 运用准经典轨线(QCT)方法, 对反应Li+HF(ν=0, j=0)→LiF+H的动力学性质进行了计算. 主要研究了不同碰撞能条件下的反应截面、转动取向、产物散射角分布和竞争反应模式等. 结果表明, 该反应存在直接提取型和间接插入型两种反应模式, 在低能量下反应以间接插入反应模式为主, 能量大于200 meV时则以直接提取反应为主.     

三维H+H2(v,j)→H2(v′,j′)+H反应中复合态生成及产物转动态分布的量子散射理论研究

用排列通道线性组合-散射波函数(LCAC-SW,linear combination of arrangement channelsscattering wavefunction)量子反应散射方法计算了H+H2(v,j)→H2(v′,j′)+H三维态-态反应几率,分析了反应体系的复合态生成(或能量共振结构),并由产物的转动态分布解释了能量共振的起源来自于平动态-内态之间的干涉效应.     

Kinetics and dynamics study of the H + CCl4?��?HCl(v��, j��)?+?CCl3 reaction

Based on a previous potential energy surface describing the H?+?CCl₄ reaction, a new analytical surface named PES-2010 was developed modifying both the functional form to give it more flexibility, and the calibration process in which exclusively theoretical information was used. Thus, the surface is completely symmetric with respect to the permutation of the four methane chlorine atoms, and no experimental information is used in the process. For the kinetics, the thermal rate constants were calculated using variational transition-state theory with semiclassical transmission coefficients over a wide temperature range, 300?C2,500?K. The theoretical results reproduce the experimental variation with temperature. The influence of the tunneling factor is small, since the abstraction reaction involves the motion of a heavy particle (a chlorine atom) that cannot easily tunnel through the reaction barrier. The coupling between the reaction coordinate and the vibrational modes shows qualitatively that the HCl stretching mode in the products appears vibrationally excited. The dynamics study was performed using quasi-classical trajectory calculations, including corrections to avoid the zero-point energy problem. First, we found that the HCl(????, j??) product mostly appears with small rotational energy and vibrational population inversion. Second, the state-specific scattering distributions show backward scattering, which becomes more noticeable as the HCl(????) vibrational state increases. Unfortunately, no experimental dynamics data are available for the title reaction, but the comparison with the kinematically similar and well-studied H?+?Cl₂ reaction shows good agreement, indicative of similar mechanisms. These kinetics and dynamics results seem to indicate that the potential energy surface is adequate to describe this reaction, and the reasonable agreement with experiment lends further confidence to this new surface.     

Quantum-dynamical study in three-dimensional space of the exchange reaction H+ClH'→HCl+H' with zero total angular momentum $ \left( {\overrightarrow J = 0} \right) $

The 3D quantum dynamics of the exchange reaction H + ClH′→HCl+H′ with zero angular momentum was studied. The nonstationary Schr?dinger equation was solved by expansion into a basis set using discrete variable representation. The probabilities of the reaction were determined in relation to the total energy for the ground and first excited vibrational states.     

Rotationally correlated reactivity in the CH (v = 0, J, F(i)) + O2 → OH (A) + CO reaction

The rotational-state-selected CH (v = 0, J, F(i)) beam has been prepared by using an electric hexapole and applied to the crossed beam reaction of CH (v = 0, J, F(i)) + O(2) → OH (A) + CO at different O(2) beam conditions. The rotational state selected reactive cross sections of CH (RSSRCS-CH) turn out to depend remarkably on the rotational state distribution of O(2) molecules at a collision energy of ～?0.19 eV. The reactivity of CH molecules in the N = 1 rotational states (namely ∣J = 1∕2, F(2)> and ∣J = 3∕2, F(1)> states, N designates the angular momentum excluding spin) becomes strongly enhanced upon a lowering of the rotational temperature of the O(2) beam. The RSSRCS-CH in these two rotational states correlate linearly with the population of O(2) molecule in the specific K(O(2)) frame rotation number states: CH(|J = 1/2,F(2)>) with O(2)(|K(O(2)) = 1>);CH(|J = 3/2,F(1)>) with O(2)(|K(O(2)) = 3>). These linear correlations mean that the rotational-state-selected CH molecules are selectively reactive upon the incoming O(2) molecules in a specific rotational state; here, we use the term "rotationally correlated reactivity" to such specific reactivity depending on the combination of the rotational states between two molecular reactants. In addition, the steric asymmetry in the oriented CH (∣J = 1∕2,?F(2),?M = 1∕2>) + O(2) (|K(O(2)) = 1>) reaction turns out to be negligible (< ±1%). This observation supports the reaction mechanism as theoretically predicted by Huang et al. [J. Phys. Chem. A 106, 5490 (2002)] that the first step is an intermediate formation with no energy barrier in which C-atom of CH molecule attacks on one O-atom of O(2) molecule at a sideways configuration.     

Theoretical Studies of O(1D)+HD (v=0, j=0, 1, 2, 3)→OD(H)+H(D) Reaction

The quasi-classical trajectory calculation for the reaction O(¹D)+HD is carried out based on the Dobbyn and Knowles potential energy surface. In this work, the reaction cross section and product branching ratio are obtained. The product branching ratio OD/OH was discussed. The calculated results show that the cross-section decreases thoroughly with the increasing of the collision energy from 4.6 kJ/mol to 46.0 kJ/mol. The average branching ratio decrease with the increase of rotational quantum number of reactant HD.