Investigation of Angular Dependence of Strong-Field Tunneling Ionization for Asymmetric Diatomic Molecule HeH2+

We determine the structure parameters for the asymmetric heteronuclear diatomic molecule HeH²⁺ at several internuclear distances with the molecular wavefunctions obtained by solving the time-independent Schrödinger equation with B-spline basis. Then the angular dependence of strong-field ionization rates of HeH²⁺ are investigated with the molecular tunneling ionization theory. We show that the shape of several lowly excited states (i.e. 2pσ ,2pπ ,3dδ ) for HeH²⁺ are reflected in the orientation dependent ionization rates very well, however, the angle-dependent ionization rate fails to follow the angular distribution of the asymptotic electron density for the ground state 1sσ . We also show that the internuclear distance dependent ionization probabilities are in a good agreement with the more accurate result obtained from the numerical solution of the time-dependent Schrödinger equation.     

Two-center interference in high-harmonic generation of H_2~+ in a combination of a mid-infrared laser field and a terahertz field

We theoretically investigate the two-center interference in high-order harmonics generated from the H_2~+ in a combination of a mid-infrared laser and a terahertz field by numerically solving the time-dependent Schr ¨odinger equation(TDSE).The interference minima in high-order harmonic generation(HHG) are effectively suppressed when a THz field is added.The contribution to HHG from the two separate nuclei is used to demonstrate the locating order of the harmonic minima.Furthermore, we also investigate the emission time of harmonics. The results show that the intensity of the short path around 60 thorder after adding a THz field is stronger than that in the mid-infrared laser field, which further illustrates the suppression of the interference minima in HHG.     

非均匀激光场中氢分子离子高次谐波的增强

通过数值求解非波恩-奥本海默近似下的一维含时薛定谔方程,研究了蝴蝶结型纳米结构基元中氢分子离子高次谐波的产生.研究表明,在蝴蝶结型纳米结构基元内部产生的非均匀场的空间位置对高次谐波的发射有较大影响.当非均匀场的空间位置从30 a.u.平移到-30 a.u.时,高次谐波的截止位置被延展且形成光滑的超连续的谐波谱,并应用时频分析方法、经典三步模型以及电离概率等解释了高次谐波发射的物理机理.研究了高次谐波谱对非均匀场空间位置的依赖性与载波包络值的关系,发现随着载波包络值的变化,非均匀场在不同空间位置处的高次谐波谱变化趋势相同.     

Laser phase effect on asymmetric harmonic distribution in H_2~+

The laser phase effect on the spatial distribution of the molecular high-order harmonic generation(MHHG) spectrum from H_2~+ is theoretically investigated through solving the Non-Bohn-Oppenheimer(NBO) time-dependent Schrodinger equation(TDSE).The results are shown as follows,(i) The generated harmonics from the two nuclei each present an asymmetric distribution.Particularly,when the laser phases are chosen from 0.0π to 0.6π and from 1.7π to 2.0π,the contribution from the negative-H plays a main role in harmonic generation.When the laser phases are chosen from 0.7πto 1.6k,the contribution from the positive-H to the harmonic generation is remarkably enhanced and becomes greater than that from the negative-H.The electron localization,the time-frequency analyses of the harmonic spectrum and the time-dependent wave function are shown to explain the asymmetric harmonic distribution in H_2~+,which provides us with a method to control the electron motion in molecules,(ⅱ) As the pulse duration increases,the asymmetric distributions of the MHHG in two H nuclei decrease,(ⅲ) Isotope investigation shows that the asymmetric harmonic distribution can be reduced by introducing the heavy nucleus(i.e.,D_2~+).     

全局耦合网络上的两种类集团的聚集-湮没反应动力学

利用Monte-Carlo模拟研究了全局耦合网络上扩散限制的不可逆聚集-湮没过程的动力学行为. 在系统中, 同种类集团相遇, 将发生聚集反应; 不同种类的集团相遇, 则发生部分湮没反应. 模拟结果表明:1) 当两种粒子初始浓度相等时, 系统长时间演化后, 集团浓度c(t)和粒子浓度g(t)呈现幂律形式, c(t)～t^{- α}和g(t)～t^-β, 其中幂指数α 和β 满足α=2β 的关系, 且α=2/(2 + q); 集团大小分布随时间的演化满足标度律, a_kt)=k^-τt^-ω\varPhi (k/t^z), 其中τ≈-1.27q, ω≈(3 + 1.27q)/(2 + q), z=α/2=1/(2 + q); 2) 当两种粒子初始浓度不相等时, 系统经长时间演化后, 初始浓度较小的种类完全湮没, 而初始浓度较大的那个种类的集团浓度c_A(t)仍具有幂律形式, c_A(t)～t^-α, 其中α=1/(1+q), 其集团大小分布随时间的演化也满足标度律, 标度指数为τ≈-1.27q, ω≈(2 + 1.27q)/(1 + q)和z=α=1/(1 + q). 模拟结果与已报道的理论分析结果相符得很好.     

Controlling the contributions to high-order harmonic generation from different nuclei of N_2 with an orthogonally polarized two-color laser field

The generation of high-order harmonic and the attosecond pulse of the N2 molecule with an orthogonally polarized two-color laser field are investigated by the strong-field Lewenstein model.We show that the control of contributions to high-order harmonic generation(HHG) from different nuclei is realized by properly selecting the relative phase.When the relative phase is chosen to be φ= 0.4π,the contribution to HHG from one nucleus is much more than that from another.Interference between two nuclei can be suppressed greatly; a supercontinuum spectrum of HHG appears from 40 e V to125 e V.The underlying physical mechanism is well explained by the time–frequency analysis and the semi-classical threestep model with a finite initial transverse velocity.By superposing several orders of harmonics,an isolated attosecond pulse with a duration of 80 as can be generated.     

The Formation Mechanism and Binding Energy for the Octahedral Central Structure of the He7^＋ Cluster

The formation mechanism for the octahedral central structure of the He7^ cluster is proposed and its total energy curve is calculated by the method of a modified arrangement channel quantum mechanics (MACQM). The energy is a function of separation R between two nuclei at the center and an apex of the octahedral central structure. The result of the calculation shows that the curve has a minimM energy -19.7296 a.u. at R = 2.40α0. The binding energy of He7^ with respect to He^ 6He was calculated to be 0.6437 a.u. This means that the duster of He7^ may be formed in the stable octahedral central structure with R=2.40 α0.     

Invariant Sets and Exact Solutions to Nonlinear Diffusion Equations with x-Dependent Convection and Absorption

In this paper, we introduce a new invariant set ˜E₀={u:u_x=f^ˊ(x)F(u)+ε [g^ˊ(x) -f^ˊ(x)g(x)]F(u)exp(-∫^u(1/F(z))dz), where f and g are some smooth functions of x, ε is a constant, and F is a smooth function to be determined. The invariant sets and exact solutions to nonlinear diffusion equation u_t=(D(u)u_x)_x+Q(x,u)u_x+P(x,u), are discussed. It is shown that there exist several classes of solutions to the equation that belong to the invariant set ˜E₀.     

ON THE HYDROGEN MOLECULAR CORRECTION TO THE TRITON β-SPECTRUM AND THE MEASUREMENT OF THE NEUTRINO MASS

By using a highly accurate variational wave function with 50 parameters for hydrogen molecule^[4] and the wave function of HeH⁺ used by Wolniewicz with 64 parameters^[5], the behavior of the β-spectrum of H-T→ HeH⁺+β^-+νe is discussed. The spectral shape thus obtained deviates remarkably from the β-spectrum of an atomic triton, and hence is different from the for mula used by Lyubimov et al. in determining the neutrino mass. This means that the "atomic approximation" is invalid in describing the molecular β-spectrum of valine, and the conclusion about the value of neutrino mass based upon the analysis of β -spectrum of valine also cannot be regarded as a reliable one. Therefore, in order to obtain ari accurate value of neutrino mass from the β-spectral shape, it is important to investigate the structure of the radioactive source, from which the corection has arisen.     

Formation Mechanism and Binding Energy for Icosahedral Central Structure of He13^＋ Cluster

The formation mechanism for the icosahedral central structure of the He13^ cluster is proposed and its total energy curve is calculated by the method of a Modified Arrangement Channel Quantum Mechanics. The energy is the function of separation R between two nuclei at the center and an apex of the icosahedral central structure. The result of the calculation has shown that the curve has a minimal energy -37.5765 (a.u.) at R=2.70ao. The binding energy of He13^ with respect to He^ 12He was calculated to be 1.4046 a.u. This means that the cluster of He13^ may be formed in an icosahedral central structure with strong binding energy.     

HeH+体系光缔合反应的动力学研究

采用含时量子波包方法研究基电子态HeH⁺体系优化的光缔合几率,即He+H⁺→HeH⁺随碰撞粒子对初始动量的变化,并研究伴随该过程的多光子跃迁和解离.选取v=6振动能级为目标态,通过优化激光场参数得到碰撞粒子对的最优光缔合几率.结果表明：随着碰撞粒子对初始动量的增加,光缔合所用的最优激光场的持续时间逐渐减少,但光场的强度和失谐逐渐增加.在某些初始碰撞动量附近,由于共振多光子跃迁过程的存在,最优的光场不能严格地将碰撞粒子对缔合到目标态.此外,研究表明随着初始动量的增加,系统的超阈值解离几率近似线性地增加到一个最大值,直至饱和强度.并且,在碰撞粒子对的初始动量较大时,超阈值解离主导解离过程.     

On Diagonal P-Representation of Superposition Field of Two Light Modes

For the superposition field a₁^†+a₂^† of two light modes we introduce an appropriate diagonal P-representation which is constructed on the common eigenvectors |z,x〉of (X₁-X₂) and a₁+a₂, where X_i=(a_i+ a_i^†)/√(2), [a_i,a_i^†] =δ_ij. It is remarkable that |z,x〉make up a new quantum mechanical representation.     

不同核轴取向的O2的高次谐波

分子的高次谐波是强场超快物理的重要研究课题. 采用建立在形式散射理论基础上的频域方法计算了O₂在线偏振激光场下的高次谐波, 探讨了核轴被准直在与激光传输方向垂直的平面内时, 高次谐波随核轴与光电场偏振方向所成夹角θ₀的依赖关系. 结果表明: 各次谐波都是在θ₀约为45°时强度最大, 并有较宽的峰值宽度; 当偏离此角度, 高次谐波的强度变小; 到达平行或垂直取向时, 降到最低. 分析表明, 这是由于高次谐波的强度取决于分子基态的电子在动量空间中的电场方向的布居. 针对核轴被准直在激光传输方向与电场偏振方向所确定的平面内的情况, 计算了高次谐波随θ₀的依赖关系, 结果与前一种情况基本相同. 分析发现, 当核轴被准直固定后, 分子绕核轴旋转的角度ψ没有固定, 所以最后的高次谐波强度需要对不同的ψ 时的高次谐波的贡献求和平均. 平均后相当于波函数相对于核轴旋转对称, 从而导致O₂的高次谐波仅与θ₀有关, 而与核轴被准直在哪个面上无关.     

Geometric structure of N2Oq+ (q = 5, 6) studied by Ne8+ ion-induced Coulomb explosion imaging

We report the study on the complete three-body Coulomb explosion (CE) of N₂O^q+ (q = 5, 6) induced by 56-keV/u Ne⁸⁺ ion collision with N₂O gaseous molecule. Six CE channels for N₂O⁵⁺ and seven for N₂O⁶⁺ are identified by measuring three ionic fragments and the charge-changed projectile in quadruple coincidence. Correspondingly the kinetic energy release (KER) and momentum correlation angle (MCA) distributions of three ionic fragments for each of the CE channels are also deduced. Numerical computation is presented to reconstruct the geometric structure of N₂O^q+ prior to dissociation based on the measured KER and MCA. The N-N and N-O bond lengths and the N-N-O bond angles of N₂O^q+ for each of the channels are determined.     

Xe~(53+)离子与Xe原子碰撞过程中的辐射电子俘获和辐射退激发光谱的理论研究

基于多组态Dirac-Fock方法和密度矩阵理论,系统地研究了在197 Me V/u的碰撞能量下,Xe~(53+)离子与Xe原子的辐射电子俘获过程(REC)以及电子被俘获到激发态后辐射退激发产生的特征谱线.计算了炮弹Xe~(53+)离子俘获电子到不同壳层np_(1/2,3/2)(n=2—5)的总截面与相应的REC光子能量和角分布,以及由激发组态1snp_(1/2,3/2)(n=2—5)J_f=1向基态1s~2Jd=0辐射退激发的跃迁能量、跃迁概率和特征光子的角分布和线性极化度.计算结果表明,辐射光子具有显著的角各向异性特征.此外,1snp_(3/2)J_f=1→1s~2J_d=0退激发特征光子也显示出很强的线性极化和角各向异性特征,而1snp_(1/2)J_f=1→1s~2J_d=0退激发特征光子的线性极化度趋于零并且角分布也趋于各向同性.     

High spin states in doubly even pf-shell nuclei

High spin states of the yrast band in ⁵⁰Ti, ⁵²Cr, ⁵⁴ and ⁴⁶Ti are investigated in a microscopic approach allowing a coupling of rotations, vibrations and quasiparticle excitations. The lowering of the 6⁺ state in N = 28 nuclei is shown to originate mainly from proton K = 0 two-quasiparticle excitations. Using as a basis the entire pf-shell 8⁺ and 10⁺ states can be predicted for ⁵⁰Ti and ⁵⁴Fe.     

THE CORRECTION OF HYDROGEN MOLECULAR EXCITATION TO THE 3T β-SPECTRUM

Using a modified variational wave function of Michels type the second excited ¹Σ state of HeH⁺ ionis calculated, and consequently its contribution to the tritium molecule β-spectrum is estimated. Inaddition to this, the source temperature effect as well as the effect of different isotopic compositions such as T₂, TD and TH in the hydrogen molecules are also discussed in detail.     

QQqq Four-Quark Bound States in Chiral SU(3) Quark Model

The possibility of QQqq heavy-light four-quark bound states has been analyzed by means of the chiral SU(3) quark model, where Q is the heavy quark (c or b) and q is the light quark (u, d, or s). We obtain a bound state for the bbnn configuration with quantum number J^P=1⁺,I=0 and for the ccnn (J^P=1⁺,I=0) configuration, which is not bound but slightly above the D^*D^* threshold (n is u or d quark). Meanwhile, we also conclude that a weakly bound state in bbnn system can also be found without considering the chiral quark interactions between the two light quarks, yet its binding energy is weaker than that with the chiral quark interactions.