H$lt;sub$gt;2$lt;/sub$gt;$lt;sup$gt;+$lt;/sup$gt;在强激光场中的解离及其量子调控的理论研究

利用非波恩-奥本海默近似的三维含时量子波包法,理论研究了氢分子离子在强激光场中的解离动力学.通过分析H₂⁺在不同的初始振动态（ν=0–9）和激光场强度下的解离核动能谱,得到了H₂⁺的光解离机理及其随激光场的变化规律.研究结果表明：当激光场的强度I₁=5.0×10¹³ W/cm²时,分子的解离来源于高振动态ν=5–9,其解离机理主要是通过键软化、键硬化和阈下解离过程.当激光场的强度I₂=1.0×10¹⁴ W/cm² 时,H₂⁺在低振动态ν=3–4上的阈上解离起主导作用,而高振动态的键软化、键硬化和阈下解离所占的比重明显地下降了.研究结果为后续的量子调控的实验研究提供了科学的理论预测和指导. 关键词： 光解离 氢分子离子 含时波包法 核动能谱     

H_2~+分子双H核对高次谐波辐射的贡献

理论研究了H_2~+分子双H核对高次谐波辐射的贡献.结果表明:在少周期激光场下,由于激光场的反对称性,负向H核辐射谐波强度高于正向H核.随着激光脉宽增大,激光波形趋于对称,因此导致双H核辐射谐波的反对称结构减小.谐波辐射的时频分析图显示,当激光场为正向时(E(t)0.0),负向H核辐射谐波强度高于正向H核;当激光场反向时(E(t)0.0),正向H核辐射谐波强度高于负向H核.最后,通过分析含时电子波包及H_2~+的缀饰态给出了电子在双H核之间转移的原因.     

H2+分子双H核对高次谐波辐射的贡献

理论研究了H2+分子双H核对高次谐波辐射的贡献。结果表明：在少周期激光场下，由于激光场的反对称性，负向H核辐射谐波强度高于正向H核。随着激光脉宽增大，激光波形趋于对称，因此导致双H核辐射谐波的反对称结构减小。谐波辐射的时频分析图显示，当激光场为正向时(E(t) > 0.0)，负向H核辐射谐波强度高于正向H核；当激光场反向时(E(t) < 0.0)，正向H核辐射谐波强度高于负向H核。最后，通过分析含时电子波包及H2+的缀饰态给出了电子在双H核之间转移的原因。     

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.     

Carrier envelope phase effect on the spatial distribution of high-order harmonic generation in asymmetric molecule

The spatial distribution in high-order harmonic generation(HHG) from the asymmetric diatomic molecule He H~(2+) is investigated by numerically solving the non-Born–Oppenheimer time-dependent Schr?dinger equation(TDSE). The spatial distribution of the HHG spectra shows that there is little contribution in HHG around the geometric center of two nuclei(z = 1.17 a.u.) and the equilibrium internuclear position of the H nucleus(z = 3.11 a.u.). We demonstrate the carrier envelope phase(CEP) effect on the spatial distribution of HHG in a few-cycle laser pulse. The HHG process is investigated by the time evolution of the electronic density distribution. The time–frequency analysis of HHG from two nuclei in HeH~(2+) is presented to further explain the underlying physical mechanism.     

N_2-H_2容性耦合等离子体电非对称效应的particle-in-cell/Monte Carlo模拟

H_2-N_2混合气体电容性耦合射频放电在有机低介电系数材料刻蚀中具潜在研究意义.采用paxticle-incell/Monte Carlo模型模拟了双频(13.56 MHz/27.12 MHz)电压源分别接在结构对称的两个电极上的H_2-N_2容性耦合等离子体特征,研究了其电非对称效应.模拟结果表明,通过调节两谐波间的相位角θ,可以改变其电场、等离子体密度、离子流密度的轴向分布及离子轰击电极的能量分布.当相位角θ为0°时,低频电极(晶片)附近主要离子(H_3~+)的密度最小,离子(H_3~+,H_2~+,H~+)轰击低频电极的流密度及平均能量最高;当θ从0°变化90°时,低频电极的自偏压从-103V到106V近似线性增加,轰击电极的离子流密度变化约±18%,H~+离子轰击低频电极的最大能量约减小2.5倍,轰击电极的平均能量约变化2倍,表明氢离子能量和离子流几乎能独立控制.     

双色场诱导气体产生相干可控的四次谐波

利用钛宝石飞秒激光器输出的基频脉冲ω及其倍频脉冲2ω所构成双色场作用空气, 实验中检测到了中心波长处于真空紫外波段的四阶谐波. 在气体未发生电离的情况下, 四次谐波强度对双色场的能力依赖关系显示其产生是参量过程2ω+ω+ω→4ω的贡献. 当气体发生电离, 四次谐波强度与双色场相对相位有关, 可通过双色场相干控制. 实验研究了四次谐波对双色场相位的依赖性以及与太赫兹波的关联性, 其结果与数值模拟结果相符, 分析发现当气体发生电离时四次谐波的产生过程存在太赫兹辐射Ω_THz的参与, 是参量过程2ω+2ω±Ω_THz→4ω和2ω+ω+ω→4ω的共同贡献.     

Generation of elliptical isolated attosecond pulse from oriented H2+ in a linearly polarized laser field

We investigate the ellipticity of the high-order harmonic generation from the oriented H₂⁺ exposed to a linearly polarized laser field by numerically solving the two-dimensional time-dependent Schrödinger equation (2D TDSE). Numerical simulations show that the harmonic ellipticity is remarkably sensitive to the alignment angle. The harmonic spectrum is highly elliptically polarized at a specific alignment angle θ=30°, which is insensitive to the variation of the laser parameters. The position of the harmonic intensity minima indicates the high ellipticity, which can be attributed to the two-center interference effect. The high ellipticity can be explained by the phase difference of the harmonics. This result facilitates the synthesis of a highly elliptical isolated attosecond pulse with duration down to 65 as, which can be served as a powerful tool to explore the ultrafast dynamics of molecules and study chiral light-matter interaction.     

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.     

用于α和μ常数变化测量的碘离子光谱研究

分子离子I_2~+的禁戒跃迁光谱有可能用于测量α和μ常数的变化,并且具有增强的灵敏度.通过分析I_2~+在11860—13100 cm~(-1)范围内的转动光谱,拟合了A~2Π_(3/2)-X~2Π_(3/2)系统31个振转带的5759根吸收谱线,得到5个属于X~2Π_(3/2)态和9个属于A~2Π_(3/2)态的振动能级准确的转动光谱常数.在量子噪声极限和1 Hz跃迁线宽的条件下,计算得到X~2Π_(3/2)和X~2Π_(1/2)之间的禁戒跃迁对α和μ常数变化测量的灵敏度为δ_(α/α)≈2.37×10~(-19)a~(-1)和δ_(μ/μ)≈1.18×10~(-18)a~(-1).     

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开发了氢气甚高频(60MHz)容性耦合放电的PIC/MC模型.在模型中考虑了带电粒子(e,H+,H2+,H3+)与H2的21种碰撞反应过程,模拟了氢气甚高频放电射频电场和电势分布以及电子和氢离子(H+,H2+,H3+)粒子密度和平均能量分布,并与频率为13.56MHz的放电结果进行了比较.结果表明,相对于频率13.56MHz的放电,氢气甚高频放电等离子体电势增高,导致两电极附近的电场增强;另外,两鞘层厚度变窄并且电子和H3+离子平均能量减小,其总密度却增加.H3+离子为氢气甚高频放电空间的主要离子,H2+离子密度比H3+离子小约2～3个数量级.     

圆筒内氢等离子体非定常化学反应羽流场DSMC分析

利用直接模拟Monte Carlo方法研究圆筒侧壁注入氢等离子体羽流场在8×10^-6s内的非定常流动特性.根据Bird的化学反应模型考虑离解-复合反应模型和电荷转移反应模型.在流场中注入H₂、H、金属原子X、H₂⁺和H⁺五种组分,研究离解-复合反应对流场中粒子分布和密度的影响,结果表明离解-复合反应使H₂数密度降低,H数密度增加,说明在流场中H₂的离解反应速率大于H的复合反应速率.加入电荷转移反应后H₂⁺数密度降低,H⁺数密度增加,对其他组分数密度没有显著影响.     

Amplitude and rotation of the ellipticity of harmonicsfrom a linearly polarized laser field

We simulate the dynamic response of H₂⁺ in a linearly polarized laser field by numerically solving the time-dependent Schrödinger equation. The elliptically polarized high-order harmonics generated by H₂⁺ irradiated by the linearly polarized laser field are systematically investigated. The result shows that the amplitude and rotation of the ellipticity of harmonics are affected by the alignment angle and internuclear distance of the molecule. Analyzing the change in forces acted on the ionized electrons and the trajectories of the electrons, the phenomena are found to be due to the change in the direction of the total Coulomb forces from the two nuclei felt by the recollided ionized electrons in the direction perpendicular to the laser polarization direction. Based on the influence law, we can select the harmonics with a specific frequency band under different alignment angles and then synthesize the isolated attosecond pulses with different rotations, which can be continuously converted from right-handed circular polarization, linear polarization, and left-handed circular polarization by changing the alignment angle. This study provides a new possible approach to the real-time detection of molecular states by using attosecond pulses and obtaining more optimized harmonics with molecular properties.     

Na_2~+离子较低电子态势能曲线和光谱常数的理论研究

通过多组态相互作用方法,结合原子有效芯势与极化势,利用非收缩的高斯基函数,计算了Na_2~+分子对应最低9个解离限的36个电子态的势能曲线.基于计算获得的束缚态势能曲线,拟合给出了相应的光谱常数,并与已有的实验和理论结果进行了比较.同时,给出了部分电子态的振动-转动能级和一些同类态避免交叉点的信息.计算获得的光谱信息对冷原子分子光谱与动力学的研究具有参考价值.     

Elastic electron scattering with formamide-(H2O)n complexes (n=1, 2): Influence of microsolvation on the π* and σ* resonances

We report elastic cross sections for low-energy electron scattering with formamide-(H₂O)_n complexes (n=1, 2) in the energy region of 0.01-8 eV. The scattering calculations are performed using the R-matrix method in the static-exchange (SE) approximation. We consider three structures of formamide-H₂O and six structures of formamide-(H₂O)₂ in the present work. Our purpose is to investigate effects of water molecules hydrogen-bonding to formamide. We focus on the influence of microsolvation on the π^* and σ^* resonances of formamide. The scattering result for complexes shows that the position of π^* resonance appears at lower or higher energies in the cluster than in the isolated formamide depending on the complex structure and the water role in the hydrogen bonding. We explain this behavior according to the net charge of the solute. It is found that the microsolvation environment has a substantial effect on the width of π^* resonance. Our results indicate that surrounding water molecules may affect the lifetime of the resonances, and hence the process is driven by the anion state, such as the dissociative electron attachment.     

利用半周期激光场调控H_2~+谐波辐射过程

采用数值求解核与电子耦合的薛定谔方程,对H_2~+分子谐波辐射调控进行了研究.计算结果表明,激光场正向时,谐波能量主要来源于负向H核贡献;激光场负向时,谐波能量主要来源于正向H核.随后,通过适当引入半周期激光场,可以有效调节正负H核辐射谐波的强度.最后,适当叠加谐波谱上的谐波,可获得一个46 as的脉冲.该研究对调控分子谐波的辐射过程及阿秒脉冲的输出是有帮助的.     

Wavelength dependence of electron localization of H_2~+ and its isotopomers in the UV-pump-probe scheme

The wavelength dependence of electron localization of H_2~+ and its isotopomers in the ultraviolet pump-probe scheme is investigated by numerically solving the time-dependent Schrdinger equation. By combining with a semiclassical method,an effective analytical formula expressed in the adiabatic representation is established to describe the localization probability with several zero crossings. A stable zone with respect to the laser intensity and carrier envelope phase is found at a relatively long probe wavelength. Finally, the critical probe wavelengths to reach at the stable zone are derived by using the three-dimensional model. Slower nuclear motion of heavier isotopomers leads to a longer critical wavelength.     

O-乙基O-芳基N-异丙基硫代磷酰胺酯类化合物的除草活性与其31P化学位移的关系

本文测定了标题所示一类化合物的³¹P的化学位移,并讨论了它与取代基电子性间存在如下的关系δP=-0.9193σ+3.5891F+66.5385提出了³¹P化学位移与此类化合物的除草活性间存在一定的相关性,其关系如下PI₅₀=-0.9025π²+0.9017π-0.5600E_s-0.1620△δP+0.8445I+4.2514并对此关系的适用性及存在偏差作了初步讨论。     

High-order harmonic generation of the cyclo[18]carbon molecule irradiated by circularly polarized laser pulse

High-order harmonic generation of the cyclo[18]carbon (C₁₈) molecule under few-cycle circularly polarized laser pulse is studied by time-dependent density functional theory. Compared with the harmonic emission of the ring molecule C₆ H₆ having similar ionization potential, the C₁₈ molecule has higher efficiency and cutoff energy than C₆ H₆ with the same laser field parameters. Further researches indicate that the harmonic efficiency and cutoff energy of the C₁₈ molecule increase gradually with the increase of the laser intensity of the driving laser or decrease of the wavelength, both are larger than those of the C₆ H₆ molecule. Through the analysis of the time-dependent evolution of the electronic wave packets, it is also found that the higher efficiency of harmonic generation can be attributed to the larger spatial scale of the C₁₈ molecule, which leads to a greater chance for the ionized electrons from one atom to recombine with others of the parent molecule. Selecting the suitable driving laser pulse, it is demonstrated that high-order harmonic generation in the C₁₈ molecule has a wide range of applications in producing circularly polarized isolated attosecond pulse.     

潘宁源放电的全三维电磁粒子模拟/蒙特卡罗碰撞数值算法研究

深入研究潘宁放电的物理机制, 研制了全三维高品质算法粒子模拟软件(PIC), 设计并添加了相应物理情景的蒙特卡罗碰撞模块(MCC), 并对电子、氢分子离子(H₂⁺)、氢正离子(H⁺)、氢三正离子(H₃⁺)同时进行了跟踪, 成功研制了全三维电磁PIC/MCC数值算法. 结合国内研究较热的潘宁放电模型, 对该算法进行模拟验证. 模拟结果显示: 采用有效的滤波算法能抑制电磁数值噪声, 电子能量呈麦克斯韦分布, 由于电子的径向漂移和加速导致离子源顶端H₂⁺产量较大. 关键词： 潘宁离子源 高品质算法 粒子模拟/蒙特卡罗