采用量子含时波包方法研究H/D+Li_2→LiH/LiD+Li反应

采用量子波包方法和二阶分裂算符方法对H/D+Li_2→LiH/LiD+Li反应在0.01到0.4 eV的碰撞能范围内进行了动力学计算.在态分辨的理论水平上计算了反应概率、积分截面、微分截面等动力学性质并与之前的理论结果进行了比较.结果表明:由于本文的计算中包含了总角动量J在体固定坐标轴上的所有投影所得,结果更加精确;此外,当H原子被重的同位素原子D取代,反应概率、积分截面增大,然而这并没有对反应机理产生大的影响.前后对称的微分截面表明插入反应机理在反应过程中占据主导地位.     

Isotope effect and Coriolis coupling effect forthe Li + H(D)Cl → LiCl + H(D) reaction

A time-dependent quantum wave packet method is used to investigate the dynamics of the Li + H(D)Cl reaction based on a new potential energy surface(J. Chem. Phys. 146 164305(2017)). The reaction probabilities of the Coriolis coupled(CC) and centrifugal sudden(CS) calculations, the integral cross sections, the reaction rate constants are obtained. The rate constants of the Li + HCl reaction are within the error bounds at low temperature. A comparison of the CC and CS results reveals that the Coriolis coupling plays an important role in the Li + H(D)Cl reaction. The CC cross sections are larger than the CS results within the entire energy range, demonstrating that the Coriolis coupling effect can more effectively promote the Li + DCl reaction than the Li + HCl reaction. It is found that the isotope effect has a great influence on the title reaction.     

Influence of reagent vibration on the stereodynamics of the Li + HF → LiF + H reaction

We investigate the influence of reagent vibration on the stereodynamics of the title reaction by the quasi-classical trajectory on the Aguado-Paniagua2-potential energy surface developed by Aguado et al. (J. Chem. Phys. 1997 106 1013). The cross sections and reaction probability as functions of the reagent vibration are calculated in the centre-of-mass frame. The product angular distributions of p(θ_r), p(φ_r), and p(θ_r, φ_r), which reflect the vector correlation, are also presented and discussed. The results indicate that the vector properties are sensitively affected by the vibrational excitation.     

Product polarization and mechanism of Li + HF(v=0, j=0) → LiF(v', j') + H collision reaction

A state-to-state dynamics analysis for the Li+HF(v=0,j=0)→LiF(v',j')+H collision reaction has been performed through quasiclassical trajectory(QCT)calculations.It is found that the differential cross section(DCS)of the LiF products from the title reaction is preferentially backward scattering for v=0,yet forward scattering for v=1 and 2.For v=3,the DCS exhibits forward,backward,and sideways scatterings.The variation of the internuclear distances and angles along the propagation time reveals that more than 99.08%of reaction trajectories undergo the direct reaction mechanism.The values of the polarization parameters a{1}1and a{2}0demonstrate that the product rotational angular moment j' is not only aligned perpendicular to the reagent relative velocity vector,but also oriented along the negative y axis.These product polarization results agree well with the recent quantum mechanical studies.The mechanism of these results was proposed and discussed in detail.     

Stereodynamics of the reactions: F+H_2/HD/HT→FH+H/D/T

Among many kinds of ways to study the properties of atom and molecule collision, the quasi-classical trajectory(QCT) method is an effective one to investigate the molecular reaction dynamics. QCT calculations have been carried out to investigate the stereodynamics of the reactions F + H2/HD/HT→FH + H/D/T, which proceed on the lowest-lying electronic states of the FH2 system based on the potential energy surface(PES) of the 12A' FH2 ground state. Although the QCT method cannot describe all quantum effects in the process of the reaction, it has unique advantages when facing a three-atoms system or complicated polyatomic systems. Differential cross sections(DCSs) and three angle distribution functions P(θr), P(φr), P(θr, φr) on the PES at the collision of 2.74 kcal/mol have been investigated. The isotope effect becomes more obvious with the reagent molecule H2 turning into HD and HT. P(θr, φr), as the joint probability density function of both polar angles θr and φr, can reflect the properties of three-dimensional dynamic more intuitively.     

Isotope effect in chemical shifts of μ+ and H+: MuBr versus HBr and MuHO versus H2O

The isotopic difference between the diamagnetic shielding of a positive muon (⁺) in ⁺ HBr and H₂O and the analogous shielding of protons is computed from first principles in free space and in Br₂ solution, using a self-consistent cellular cluster multiple scattering method (SC-CMS) for condensed matter and for the free molecules. The isotope shift of the chemical shift _is at the ⁺ in these molecules dissolved in liquid Br₂ is evaluated with the eigenfunctions and eigenvalues obtained using Ramsey's formalism. For HBr the computed chemical shifts _is are comparable with experiment and with the calculations of Breskman and Kanofsky and of Williams, and the solvent effect has the correct sign and order of magnitude. For H₂O, _is has also the correct sign and order of magnitude when compared with ⁺SR experiments.     

Stereodynamics study of reactions N(~2D)+HD→NH+D and ND+H

The product polarizations of the title reactions are investigated by employing the quasi-classical trajectory (QCT) method. The four generalized polarization-dependent differential cross-sections (PDDCSs) $({2\pi } / \sigma )(\d\sigma _{00} / \d\omega _t )$, $({2\pi } / \sigma )(\d\sigma _{20} / \d\omega _t )$, $({2\pi } / \sigma )(\d\sigma _{22 + } / \d\omega _t )$, and $({2\pi } / \sigma )(\d\sigma _{21 - } / \d\omega _t )$ are calculated in the centre-of-mass frame. The distribution of the angle between ${{\bm k}}$ and ${{\bm j^\prime }}$, $P(\theta _r )$, the distribution of the dihedral angle denoting ${{\bm k}}${--}$\bm k^\prime $--$\bm j^\prime $ correlation, $P(\phi _r )$, as well as the angular distribution of product rotational vectors in the form of polar plots $P(\theta _r ,\phi _r )$ are calculated. The isotope effect is also revealed and primarily attributed to the difference in mass factor between the two title reactions.     

Isotopic Effects on Stereodynamics of the C~+ + H_2→CH~+ + H Reaction

The effects of isotope substitution on stereodynamic properties for the reactions C~+ + H_2/HD/HT →CH~+ + H/D/T have been studied applying a quasi classical trajectory method occurring on the new ground state CH_2~+ potential energy surface [J. Chem. Phys. 142(2015) 124302]. In the center of mass coordinates applying the quasi classical trajectory method to investigate the orientation and the alignment of the product molecule. Differential cross section and three angle distribution functions P(θ_r), P(ф_r), P(θ_r, ф_r) on the potential energy surface that fixed the collision energy with a value is 40 kcal/mol have been studied. The isotope effect becomes more and more important with the reagent molecules H_2 changing into HD and HT. P(θ_r, ф_r) as the joint probability density function of both polar angles θ_r and ф_r, which can illustrate more detailed dynamics information. The isotope effect is obvious influence on the properties of stereodynamics in the reactions of C~+ + H_2/HD/HT → CH~+ + H/D/T.     

Isotope Effects in the Spectra of Hydrogen-Bonded Complexes. Anharmonic Calculations of Isotopologues of the [F(HF)2]– Complex

Optics and Spectroscopy - The frequencies and intensities for IR absorption bands of symmetric and asymmetric hydrogen-bonded complexes [FL1FL2F]– (L1, L2 = K-meson Ka, proton H, deuteron D,...     

Semiclassical and quasiclassical calculation of reaction probabilities for collinear X + F2→XF + F (X = Mu,H, D,T)

Semiclassical calculations of reaction probabilities have been carried out for the collinear H + F₂ (n = 0, 1) reaction using the best extended LEPS surface No. II of Jonathan et al. Both real and complex valued classical trajectories have been included in the calculations for an energy range where the quasiclassical total reaction probability is unity. Comparison with quantum results shows the semiclassical reaction probabilities are accurate to about ± 0·05 provided only two real or complex stationary phase points make an important contribution to the S matrix element, so that the uniform Airy or integer Bessel approximations are valid. Real semiclassical calculations are also reported for the collinear Mu, D, T + F₂ (n = 0) reactions. For the D and T reactions, the semiclassical reaction probabilities are estimated to be accurate to ± 0·05, except close to the reaction threshold, but for the Mu reaction the estimated errors are much larger. In addition, quasiclassical calculations for the reaction probabilities have been carried out using half integer boxing and smooth sampling methods to quantize the product distributions. For the H + F₂ reaction, there are usually systematic deviations from the quantum reaction probabilities and the same is expected to be true for the Mu, D and T reactions.     

Effects of Final State Interactions in Pure Annihilation Decay of B+ → D+K0*

The decay of the B ⁺ meson to the D ⁺ and K ⁰* mesons is a pure annihilation decay. For this reason, in the framework of the quantum chromodynamics factorization (QCDF) approach, this decay has a small amplitude and a small branching ratio. In this research we find that, before the D ⁺ and K ⁰* mesons are produced in the final states, pair mesons such as D _s ⁺* and D _s ⁺ρ⁰ are produced. The intermediate-state mesons via the exchange of K ⁰(K ⁰*) and D ⁺(D ⁺*) go to the D ⁺ and K ⁰* final state mesons. However we calculate the B ₊ → D ⁺ K ⁰* decay in two different frameworks. The first framework is the QCDF method and the second one is final state interaction (FSI). The experimental branching ratio of B ₊ → D ₊ K ⁰* decay is less than 3 × 10^–6, and our results obtained by the QCDF method and FSI are (0.35 ± 0.04) × 10^–6 and (2.94 ± 0.10) × 10^–6, respectively.     

Direct mapping of insertion reaction dynamics: S(1D)+H2→SH+H

The Doppler-selected time-of-flight method was applied to map out the differential cross sections of the title reaction at two collision energies in a crossed-beam experiment. Roughly symmetric and highly forward–backward peaking angular distributions were observed at both energies. Vibrational structures of the SH product were resolved from the velocity measurements of the counter-product H-atom. Most of the angle-integrated observables can readily be understood on statistical grounds, which suggests that statistics plays the dominant role in determining the outcomes of this prototypical insertion reaction. In terms of more detailed angle-specific reaction attributes, significant discrepancies from statistical considerations were revealed, indicative of some hidden dynamics being buried under the statistical factor. Received: 26 February 2000 / Revised version: 20 April 2000 / Published online: 13 September 2000     

Control of photoassociation reaction F+H→HF with ultrashort laser pulse

The laser-induced vibrational state-selectivity of product HF in photoassociation reaction H+F$\rightarrow$HF is theoretically investigated by using the time-dependent quantum wave packet method. The population transfer process from the continuum state down to the bound vibrational states can be controlled by the driving laser. The effects of laser pulse parameters and the initial momentum of the two collision atoms on the vibrational population of the product HF are discussed in detail. Photodissociation accompanied with the photoassociation process is also described.     

Quasiclassical dynamics of light + heavy-heavy atom reactions: the reaction X + F2 → XF + F (X = Mu,H, D,T)

Quasiclassical trajectory calculations have been carried out for the collinear reaction X + F₂(v = 0, 1) → XF + F (X = Mu, H, D, T) using the best extended LEPS surface No II of Jonathan et al.. The behaviour of individual trajectories has been used to find the regions of the potential surface that are important for determining the total reaction probability. The bottleneck close to the saddle point and repulsive wall of the exit valley are found to be the important dynamical regions of the surface. Comparison is made with other quasiclassical calculations for light + heavy-heavy atom reactions and with quantum calculations.     

Energy and angular distributions of deuterons from the D + D → p + n + d reaction

The energy and angular distributions of deuterons from the D + D → p + n + d reaction are experimentally and theoretically studied. The experiment is conducted on the U-240 cyclotron at the Institute for Nuclear Research in an extracted beam of deuterons with energy E _D = 36.9 MeV. A theoretical analysis has been performed using the microscopic diffraction nuclear model, within which the final-state interaction is considered and simple expressions for internal wave functions and approximations that include quasibinary mechanisms are employed.     

High Resolution Crossed Beams Scattering Study of the F+HD→DF+H Reaction

采用高分辨的氢原子里德堡态标识的飞行时间谱技术,对F+HD→DF+H反应进行了交叉分子束研究. 在2.51～5.60 kJ/mol的8个碰撞能下,测得了部分转动态分辨的微分截面. 实验结果显示,反应产物角分布表现出显著的后向散射,随着碰撞能的提高,角分布会逐渐变宽. 确定了产物振动态分支比随碰撞能变化的关系. 结果显示产物DF表现出高度振动态反转布居,其中DF(v′=3)态是布居数最高的产物态,在3.97 kJ/mol以上还探测到产物DF(v′=1)的信号.     

Kinetics and dynamics of the S(1D2) + H2 → SH + H reaction at very low temperatures and collision energies

We report combined studies on the prototypical S(1D2) + H2 insertion reaction. Kinetics and crossed-beam experiments are performed in experimental conditions approaching the cold energy regime, yielding absolute rate coefficients down to 5.8 K and relative integral cross sections to collision energies as low as 0.68 meV. They are supported by quantum calculations on a potential energy surface treating long-range interactions accurately. All results are consistent and the excitation function behavior is explained in terms of the cumulative contribution of various partial waves.     

Ab initio dynamics of the He + H+ 2 → HeH+ +H reaction: a new potential energy surface and quantum mechanical cross-sections

The reaction He + H⁺ ₂(v,j = 0) → HeH⁺(v′ = 0, j′) for v = 0, 1,2 and 3 and for scattering energies near the threshold (0.95–1.15 eV) has been studied by calculating ab initio points at MRCI level and ‘exact’ integral quantum reactive cross-sections. More than 1400 nuclear geometries have been chosen to cover the most important regions for the dynamics, an extended set of points being taken directly on a hyperspherical coordinate grid. A many-body expansion with a large number of terms permits an accurate analytical representation of the potential energy surface with a root-mean-square deviation <12meV. The hyperquantization algorithm has been extended to obtain quantum mechanical integral cross-sections which are compared with previous calculations and with experimental results.