Surface Corrugation in Rotational and Diffractive Scattering of O2 from LiF (001)

A quantum dynamic calculation on a five-dimensional O₂/LiF (001) model system is performed using the multi-configuration time-dependent Hartree method. The obtained results show that the mechanism of rotational and diffractive excitation in details: Comparison with the rotational excited state, the initially non-rotational state is seen to favor the inelastic scattering in the rotational excitation process. The surface corrugation can damp the quantum interferences and produce a greater amount of rotational inelastic scattering at the expense of the elastic process in the rotational excitation process. The diffraction process and the average energy transferred into the rotational and diffractive mode are also discussed.     

He-O_2转动激发截面的理论计算

用公认精确的密耦 (Close Coupling)方法、采用两种不同的相互作用势计算了He -O2 碰撞的态 态转动激发截面 (E =2 6.8meV) ,通过系统研究和计算发现 :低能散射时 ,He -O2 碰撞的弹性散射主要发生在小角部分 ,而非弹性转动激发主要发生在大角部分。研究表明 :转动激发截面对势能表面的方向性和散射角都非常敏感。     

Kinetic electron excitation in atomic collision cascades

The kinetic excitation of electrons upon bombardment of a solid surface with energetic ions is investigated. Using a metal-insulator-metal junction, hot electrons produced by the projectile impact are detected with excitation energies well below the vacuum level. The results provide information that cannot be accessed by electron emission experiments. The observed tunneling current depends on the projectile energy and the bias voltage across the junction, opening the possibility of internal excitation spectroscopy.     

Curvature dependence of surface phonon and plasmon frequencies

Non-retarded surface collective excitations (optical phonons and plasmons) are investigated in solids of general shape, and their polarization eigenmodes and frequencies are found. The cases of prolate and oblate spheroids and rotational paraboloids are studied in detail. The coupling of a charged particle to surface excitations is treated in the Hamiltonian formalism. Its spatial variation is studied, especially its dependence on the relative particle position with respect to the local surface curvature, which determines the contribution of each surface mode to the overall excitation spectrum in charged-particle — surface scattering.     

Subsurface-channeling-like energy loss structure of the skipping motion on an ionic crystal

The skipping motion of Ne+ ions in grazing scattering from the LiF(001) surface is studied for velocity below 0.1 a.u. with a time-of-flight technique. It is demonstrated that suppression of electronic excitation and dominance of optical phonon excitation in the projectile stopping results in an odd 1,3,5,... progression of the energy loss peaks, a feature usually ascribed to subsurface channeling. The experimental findings are well reproduced by parameter-free model calculations where thermal vibrations are the dominant cause for the ion trapping and detrapping.     

利用半经典微扰理论研究H－H_2O的非弹性碰撞—H_2O的转动、振动激发

利用半经典微扰理论计算了在Ｈ－Ｈ２Ｏ的非弹性碰撞中的Ｈ２Ｏ分子的转动、振动激发，并将计算结果与实验结果进行比较。计算中采用了Ｓｃｈａｔｚ和Ｅｌｇｅｒｓｍａ的半经验势能面，水分子的势函数，包括了谐振和非谐振力函数，在考虑了振动和转动耦合的情况下，通过半经典微扰理论来确定水分子末态的振动量子数。在Ｌｏｖｅｊｏｙ等人最近进行的实验中，当热氢原子入射时，水分子的转动和振动被激发了，而且发现水分子的转动角动量有垂直于水分子平面优先激发的趋势。我们的计算也得到出了相同的结果。     

He-Na2体系低温下的冷碰撞研究

在已经拟合好的He-Na₂体系势能面上,根据原子-双原子分子的非反应性碰撞动力学的相关基本理论,在空间固定坐标系下,采用严格的密耦方法求解了He原子和Na₂分子的转动非弹性碰撞动力学方程.并对He-Na₂体系的微分散射截面、积分截面作了详细的分析,结果与实验符合得比较好.结果表明：（1）弹性散射（Δj=0）截面远大于非弹性截面;（2）较小Δj的跃迁主要产生前向散射,随着Δj的增加,后向散射的几率增加 关键词： 2体系')" href="#">He-Na₂体系 密耦方法 微分散射截面 积分截面     

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.     

Adsorbate motions induced by vibrational mode coupling

Adsorbate motions are discussed with a primary attention focused on the coupling between a vibrational mode excited by ultrafast laser heated hot-electrons or by inelastic tunneling electrons with scanning tunneling microscope and the reaction coordinate (RC) mode. Recent experimental results have demonstrated an efficient reaction pathways involving an indirect excitation of a frustrated translational mode, rather than its direct excitation for adsorbate hopping on surfaces. Elementary processes are briefly described for hopping of CO molecules on a laser heated stepped Pt surface, where excitation of the frustrated rotation mode has been found to plays an indispensable. Calculation of the inelastic tunneling current (ITC) for excitation of the C-O stretch mode of a CO molecule is combined with a theory of anharmonic mode coupling to activate the frustrated translation mode above the barrier. The hopping rate as a function of the bias voltage agrees with the experimental result. An unified theory of single-, and two-electron processes for ITC-induced motions induced by an indirect excitation of the RC-mode via mode coupling is also applied to reproduce a crossover from hopping to desorption of a single NH₃ molecule on Cu(1 0 0) with an increase in the tunneling current.     

The stereodynamic properties of the F+HO(v,j) → HF+O reaction on~1 A' and ~3A' potential energy surfaces by quasi-classical trajectory calculations:Initial excitation effect(v=1-3, j=0 and v= 0, j=1-3)

The stereodynamic properties of the F ＋ HO （v, j） reaction are explored by quasi-classical trajectory （QCT） calculations performed on the 1At and 3At potential energy surfaces （PESs）. Based on the polarization-dependent differential cross sections （PDDCSs） and the angular distributions of the product angular momentum with the reactant at different values of initial v or j, the results show that the product scattering and product polarization have strong links with initial vibrationalrotational numbers of v and j. The significant manifestation of the normal DCSs is that the forward scattering gradually becomes predominant with the initial vibrational excitation increasing, and the scattering angle of the HF product taking place on the 3At potential energy surface is found to be more sensitive to the initial value of v. The product orientation and alignment are strongly dependent on the initial rovibrational excitation effect. With enhancement in the initial rovibrational excitation effect, there is an overall decrease in the product orientation as well as in the product alignment either perpendicular to the reagent relative velocity vector k or along the direction of the y axis, for which the initial rotational excitation effect is much more noticeable than the vibrational excitation effect. Moreover, the initial rovibrational excitation effect on the product polarization is more pronounced for the 3At potential energy surface than for the 1At potential energy surface.     

O_2－Ag（111）表面散射经典轨道研究

利用分子动力学方法，采用三体简化模型及刚性转子近似，模拟计算了同核双原子分子Ｏ２小角度入射Ａｇ（１１１）表面，分子碰撞诱导解离几率，结果与实验规律一致。同时也获得了入射分子取向效应及散射分子的角分布对碰撞能的依赖关系等动力学信息。     

Multiple electromagnetic excitation with relativistic heavy ions

The multiple electromagnetic excitation with fast projectiles (heavy ions) is studied theoretically in the sudden approximation. Of special interest is the excitation of rotational states coupled to giant (dipole) vibrations. Closed form expressions are obtained for the excitation of a rigid rotor. The strong pulse of high energy equivalent photons in relativistic heavy ion collisions opens up new possibilities for nuclear structure studies, not possible e.g. with electron scattering or nuclear Raman scattering. It is also pointed out that the “Brink-hypothesis” can be investigated in a new way by means of multiple electromagnetic excitation with relativistic heavy ions of low lying states coupled to the giant dipole mode.     

NO(ν = 1) scattering from Ag(111)

Application of laser excitation and detection techniques has allowed us to perform state-specific studies of the scattering of a molecular beam of vibrationally excited NO molecules from a Ag(111) surface. State-specific angular and velocity distributions have been obtained which indicate a direct-inelastic type of scattering mechanism. This information is combined with rotational and electronic (spin-orbit) distributions to determine the probability for survival of vibrational excitation, SP = 0.9.     

The stereodynamic properties of the F + HO (v,j)→HF + O reaction on the 1A' and 3A' potential energy surfaces by quasi-classical trajectory: Initial excitation effect (v =1-3, j = 0 and v = 0, j =1-3)

The stereodynamic properties of the F + HO (v, j) reaction are explored by quasi-classical trajectory (QCT) calculations performed on the ¹A' and ³A' potential energy surfaces (PESs). Based on the polarization-dependent differential cross sections (PDDCSs) and the angular distributions of the product angular momentum with the reactant at different values of initial v or j, the results show that the product scattering and product polarization have strong links with initial vibrational-rotational numbers of v and j. The significant manifestation of the normal DCSs is that the forward scattering gradually becomes predominant with the initial vibrational excitation increasing, and the scattering angle of the HF product taking place on the ³A' potential energy surface is found to be more sensitive to the initial value of v. The product orientation and alignment are strongly dependent on the initial rovibrational excitation effect. With enhancement in the initial rovibrational excitation effect, there is an overall decrease in the product orientation as well as in the product alignment either perpendicular to the reagent relative velocity vector k or along the direction of the y axis, for which the initial rotational excitation effect is much more noticeable than the vibrational excitation effect. Moreover, the initial rovibrational excitation effect on the product polarization is more pronounced for the ³A' potential energy surface than for the ¹A' potential energy surface.     

Highest rotational and vibrational excitation of swift diatomic molecules scattered by solid surface

It is shown that at nondissociative scattering of swift molecules by solid surface and inverse population of the highest rotational and some vibrational states unattainable at thermal excitation could be achieved. For single crystal surface a specific polarization and orientational effects in rotational and vibrational excitation of the scattered molecules could be observed.     

Molecular motions in liquid ethane studied by cold neutron scattering

In a previous work we report a comparative study of the molecular motions in gaseous and liquid methane and argon. In the present work we present the results of a study of the molecular motions in liquid ethane at three widely different temperatures. The aim is to study the rotational-translational motions of the rigid molecule. The unknown scattering from the librational and other motions of the CH₃ group is experimentally determined from a high-temperature run by a procedure of isolation of this scattering by use of successive approximations in which also the corrections for multiple scattering are involved.It is found that the translational motions are very nearly described by a cross section based on simple Langevin diffusion. The effects of encaging in ethane well below the critical point seem to influence the cross section only rather modestly. The scaling of the “encaging part” of the translational motion from liquid argon to ethane by use of the law of corresponding states is not successful. The rotational motions are equally well described by the Langevin rotational-diffusion model or by the step model. It is observed that certain degrees of rotational freedom tend to be frozen when the freezing point is approached.     

基于4A"势能面研究C(3P)+NO(X2Π)→CO(X1Σ+)+N(4S)反应的立体动力学性质

运用准经典轨线方法(QCT), 基于Abrahamsson等构造的⁴A"势能面(Abrahamsson E Andersson S, Nyman G, Markovic N 2008 Phys. Chem. Chem. Phys. 10 4400), 在碰撞能为0.06 eV时, 对C(³P)+NO(X²Π )→CO(X¹Σ⁺)+N(⁴S)反应立体动力学性质进行了理论研究. 在考虑反应物NO转动和振动激发的条件下, 计算了质心坐标系下k-j'矢量(k与j'分别为反应物速度与产物角动量)相关的P(θ_r)分布和k-k'-j'矢量(k'为产物相对速度)相关的P(φ_r)分布. 此外还计算了该反应的三个极化微分截面(2π/σ)(dσ₀₀/dω_t), (2π/σ)(dσ₂₀/dω_t)以及(2π/σ)(dσ₂₂+dω_t). 计算结果表明转动和振动激发对产物取向影响较大而对定向影响较小; 对于三个极化微分截面, 转动激发的影响不大, 而振动激发的影响则较大.     

Dynamics of water molecules adsorbed by silica and resin SGK-7

This paper has presented neutron spectroscopy data on the dynamics of light water molecules adsorbed in the cation exchanger (ion-exchange resin) SGK-7 and on the surface of aerosils (highly dispersed pyrogenic silica) with different levels of hydration. The measurements have been performed on a DIN-2PI spectrometer (Frank Laboratory of Neutron Physics of the Joint Institute for Nuclear Research, Dubna, Russia). The characteristics of the diffusive and vibrational motions of adsorbed water molecules have been determined from the experimental neutron scattering spectra. The data obtained in the quasi-elastic neutron scattering region have been analyzed using a model accounting for the effects of restricted translational and rotational diffusion. The results have demonstrated a significant decrease in the diffusion mobility of adsorbed water molecules as compared to conventional (bulk) water. In particular, the self-diffusion coefficient decreases several times, and the diffusion rate is the lower, the smaller is the thickness of the hydration layer. The dependences of the intensity and half-width of the quasi-elastic scattering peak on the magnitude of the neutron momentum transfer q in the scattering process exhibit a nonmonotonic character. This indicates manifestation of the effects of restricted translational diffusion, rotational diffusion, and jump diffusion. The partial distributions of vibrational frequencies of hydrogen atoms of water molecules adsorbed by the cation exchanger and aerosils have been obtained from the inelastic neutron scattering data.