红外光激发作用下分子导电纳米结的非弹性电流研究

将"金属-单分子-金属"模型化为分子导电纳米结,应用扩展主方程方法研究了红外光激发作用下弱耦合分子导电纳米结的非弹性电流的传导过程.分别采用偶极跃迁的指数耦合、平方耦合以及线性耦合模型描述红外光场与分子的相互作用,研究了不同光场作用下非弹性电流与所加电压的关系,并讨论了分子内振动能重新分布效应对电流-电压特性的影响. 关键词： Franck-Condon阻滞 非弹性电流 电流-电压特性 红外光激发     

光激发下分子纳米结中电荷输运的振动效应研究

在纳米金属电极和分子组成的分子纳米结中,应用分子振动的简正坐标在弱耦合近似下研究了在光激发作用下电荷的输运过程,并从电离能的角度分析了顺序电荷转移的机理,研究了在光激发条件下分子纳米结的电流-电压特性. 发现分子的振动效应是Franck-Condon阻滞在光激发作用下消失的关键因素,进而在理论上分析了分子的电离能在电荷输运中的作用,同时分析了IVR效应对光激发下分子纳米结中电荷输运的影响. 关键词： Franck-Condon阻滞 振动效应 电流-电压特性     

外场对分子纳米结电流-电压特性的影响

针对由金属电极/分子/金属电极组成的分子纳米结,应用扩展主方程的方法,考虑分子纳米结中影响其传输过程的外场、分子内的弛豫过程等因素研究了在外场作用下分子纳米结内的稳定电流和瞬间电流.由于分子内较强的电子-振动耦合,分子纳米结中的电流-电压曲线呈现台阶式非弹性特征.在不同的高斯型脉冲的激发作用下,分子纳米结中电流需要达到稳定的时间也不相同,脉冲宽度在1ps时瞬间电流现象明显,这时分子处于非平衡分布,分子两端的电流存在较大差异.随着脉冲宽度和外场偏压的增加,分子两端的电流趋于平衡.     

用CS2分子研究振动局域态的纠缠和能量

研究CS₂费米共振耦合振动局域态的Neumann纠缠熵动力学, 并研究伸缩与弯曲振动的相互作用能量, 目的是建立纠缠与能量的联系. 结果表明伸缩振动局域态的纠缠与能量是反关联更明显, 而弯曲振动局域态的纠缠与能量是正关联更明显. 还讨论了非局域态的纠缠与能量的关系.     

PTCDA分子基态的飞秒激光控制研究

将优化控制理论和多组态含时Hartree（MCTDH）方法相结合,建立了适合于MCTDH方法的计算具有平面结构的PTCDA分子的多自由度振动量子模型,研究了在PTCDA分子激发后从分子激发态回落至分子基态的动力学过程.在理论上分析了约化目标态产生率与激发脉冲、分子的演变时间及优化场的有效能量之间的关系,对分子在各个振动坐标下波函数的振动分布做了分析与比较.研究发现,增加分子的回落演变时间在提高目标态产生率的同时可以使优化激光控制场的强度降低,这为实验上用低能量激光最大程度地实现目标态提供了有效手段. 关键词： PTCDA 多组态含时Hartree方法 飞秒激光控制     

表面等离极化激元对电荷输运影响的自洽场理论研究Ⅱ——MIM体系分子轨道场的计算与分析

采用自洽场方法计算MIM体系在电场作用下分子场系数、态密度和局域电子态密度的变化.结果表明，分子场系数分布呈现弦函数形式；随电场增大，能带向深能量延伸并且能级峰间分离的更明显，以及构成电流通道的3d_m群原子轨道交叠态的重叠量增大，提高 了电荷输运的能力.该分析为探讨SPP对电荷输运影响的建立奠定了基础. 关键词： 分子轨道场系数 电流通道 态密度 局域电子态密度     

一维介观环中持续电流的电子-声子相互作用非经典效应

基于声子相干态功效和计及声子压缩态非经典效应,研究了电子-磁振子和电子-声子相互作用对一维介观环持续电流的影响. 与自由环比较,由于电子-磁振子相互作用,持续电流的振幅呈现指数减小. 对于正常态电子,电子-声子相互作用导致持续电流以Debye-Waller(D-W)因子衰减.但是计入跳步电子-单声子相干态关联效应导致系统本征态能量大幅度下降,从而持续电流I_n有大幅度增加.另一方面计入双声子相干态行为,由于声子压缩态效应压缩电子-相干(态)声子弹性散射行为,导致电子绕环运 关键词： 持续电流 电子-声子相互作用 声子相干态 声子压缩态效应     

扫描隧道显微术中的微分谱学及其应用

文章介绍了扫描隧道显微术中微分谱学的原理及其在实验中的诸多应用。微分谱（dI／dV谱）和dI／dV成像可用来研究电子局域态密度在能量和空间的分布，即微分谱固定空间一点，反映电子态密度以能量为变量的分布；而dI／dV图像则反映某给定能量的电子局域态密度以空间为变量的分布，二次微分谱（d^2I／dV^2谱）和二次微分成像可以用来反映分子的非弹性隧穿过程，从而研究分子的振动态。     

结合n模式表示势的含时密度矩阵重正化群求解激发态非辐射衰减速率：理论形式和在薁分子中的应用

本文提出一种来计算多原子分子包含Franck-Condon区势能面非谐效应的无辐射衰减速率的方法. 这种方法结合了n模式表示法,通过构造第一性势能面和近乎精确的含时密度矩阵重正化群法(TD-DMRG),来模拟量子动力学过程. 另外,在TD-DMRG 的框架下,进一步发展了计算末态分辨的速率常数的算法,它对于分析每个振动模式对于跃迁过程的贡献十分有用. 本文采用这种方法研究了考虑基态势能面非谐性后的薁分子的内转换过程. 结果表明,即使对这个半刚性的分子,模式内的非谐性也能够显著的提高内转换速率;在考虑双模式的耦合之后,速率会进一步增加. 其原因是由于C-H振动的黄昆因子接近于0,其在简谐势能面上无法对内转换做出贡献,而非谐性打开了C-H振动接受电子能量的能力.     

金属电极对有机分子非弹性电子隧穿谱的影响

利用第一性原理计算金属电极下1,6-己二硫醇和1,4-二巯基苯分子结的非弹性电子隧穿谱,发现非弹性电子隧穿谱对金属电极的变化十分灵敏,并且非弹性电子隧穿谱的振动峰位置和强度与硫原子和金属电极表面的距离密切相关.结果表明电极材料和分子与金属成键的情况是影响分子结的非弹性电子输运的重要因素.理论分析进一步表明不同金属电极和有机分子的耦合能不同导致了谱峰强弱的调整.     

To the quantum theory of chemical activity of the surface of transition metals

The dissociation of a gas molecule and the formation of a new chemical bond upon adsorption of this molecule on the surface of a transition metal are studied using the method of equations of motion. It is shown that both processes involve the formation of a mixed intermediate state during the adsorbate-substrate interaction. The dissociation is caused by a resonance growth of the vibrational mode, whereby the dissociation barrier is determined by the hybridization energy and by the frequency of electron transitions between molecular levels and the d electron energy levels of the metal in the mixed intermediate state. The resonance conditions for the formation of new surface structures are established.     

电子与氢及其同位素分子碰撞的非解离性电离截面研究

在边界等离子体中, 氢及其同位素分子与高能电子碰撞可发生电离反应. 对于尚无可利用的氢及其同位素分子的电子碰撞非解离性电离反应截面, 基于莫尔斯函数、弗兰克-康登原理, 采用半经典的Gryzinski方法进行了计算. 得到反应截面随电子能量的变化情况以及振动能级对反应截面的影响. 计算结果表明分子的振动激发对电离反应有着显著影响.     

Vibrational excitation of a molecule by a resonance current

Correct expressions are obtained for calculating a tunnel-resonance current through molecules. The participation of molecular vibrations in the resonance charge transfer through a molecule and vibrational excitation of the molecule are determined by the reorganization energy E _r of the vibrational system depending on the displacement of the equilibrium position of vibrational modes in passing from the neutral molecule to the resonance state of a molecular ion. The mean excitation energy of the molecule during the propagation of an elementary charge changes from E _r at the voltage across electrodes close to the threshold up to 2E _r at voltages considerably exceeding the threshold voltage. An expression is obtained for the stationary vibrational temperature of the molecule, which is proportional to the resonance current.     

Predissociation and the vibrational spectrum of molecular oxygen in an intense laser field. A Schumann-Runge band interval

The probabilities of predissociation and vibronic transitions between the states of the oxygen molecule in the Schumann-Runge band in the presence of a strong laser field are examined. The interaction of the molecule with the laser field is described using the rotating wave approximation. The predissociation probabilities for the avoided crossing of two adiabatic molecular terms are calculated within the framework of the Landau-Zener model. The energies of the vibrational states in the laser field are determined by diagonalization of the adiabatic Hamiltonian in the harmonic oscillator basis set. The predissociation thresholds are determined and the Franck-Condon factors are calculated as functions of the frequency and intensity of the external electromagnetic field.     

Theoretical Exploration of the Isotopic Effect on Molecular High-Order Harmonic Generation

The isotopic effect on the generation of the molecular high-order harmonics is studied by numerically solving the one-dimensional time-dependent Schrödinger equation when the model hydrogen molecule ions/hydrogen deuterium molecule ions are exposed to an intense laser pulse. To explain the effect more clearly, not only the ionization probabilities but also the electron–nuclear probability density distributions and time-frequency profiles are calculated. The results show that more intense harmonics are generated in the asymmetric diatomic molecule ions/hydrogen deuterium molecule ions than those of hydrogen molecule ions. Moreover, the interference minimum in the harmonic spectra is investigated by adjusting the laser intensity and the initial vibrational state. It is shown that the interference minimum is sensitive to the laser intensity and the initial vibrational level for hydrogen molecule ions; in contrast, it is only dependent on the initial vibrational level for hydrogen deuterium molecule ions.     

The angular behaviour of electrons inelastically scattered from the shape resonance for CO chemisorbed on Ni(110)

Recent vibrational high resolution electron energy loss experiments (HREELS) have shown evidence for molecular shape resonances in the inelastic scattering of electrons from chemisorbed molecules. Such resonances arise from the capture of the incident electron in a quasibound state of the molecule, leading to the formation of a temporary negative ion. They are manifest as an enhancement in the intensity of a specific vibrational mode at a characteristic incident electron energy. In contrast to gaseous species, the alignment which the surface provides for the chemisorbed species, can be exploited to determine the angular characteristics of the resonant state. In this work, we show evidence for a shape resonance, centred at an incident energy of 18 eV, for CO/Ni(110). The angular dependence of the scattered electron intensity has been measured for the CO stretching vibration. The results are discussed in terms of the spherical harmonic components of the resonant state, modified by vibrational broadening caused by low frequency bending modes associated with the bonding of the CO molecule to the surface.     

S2O‾自由基光电子能谱的Franck-Condon分析

本文考虑多振动模混合和热带效应,凭借谐振子模型,推得计算两维-四振动模Franck-Condon重叠积分的解析表示,且应用于S2O‾ 自由基光电子能谱的理论研究。对于S2O( 1A′) – S2O‾( 2A″) 光脱附过程,结合分子轨道从头算和密度泛函理论,计算Franck-Condon因子,从而得到电子跃迁振动谱线的相对强度,理论上得到的光电子能谱与实验上观测到的能谱达到较好的一致;进一步在光谱模拟过程中,拟合实验能谱得到可靠的负离子自由基S2O‾电子态（ 2A″）的几何结构参数：键长R(SS) = 2.008 +/-0.005Å 和 R(SO) = 1.519+/-0.005Å.     

Prospects for the formation of ultracold ground state polar molecules from mixed alkali atom pairs

Photoassociation rates of mixed cold alkali atom pairs and formation rates of cold heteronuclear alkali dimers in their ground state are computed within an approach where the wave functions are calculated exactly, and the laser field is treated as a perturbation. These rates are predicted to have the same magnitude for all heteronuclear species involving either Rb or Cs atoms. Moreover, these rates are found slightly smaller than, or similar to, the same rates for Cs₂ molecules, which is encouraging for future experiments. We studied the specific case of the photoassociation into excited molecular states coupled with spin-orbit interaction, emphasizing the role of the so-called resonant coupling in the formation of stable ultracold molecules with low vibrational levels. The comparison with recent experimental results on RbCs photoassociation and cold molecule formation show their reasonable agreement with our calculations.Received: 2 July 2004, Published online: 23 November 2004PACS: 32.80.Pj Optical cooling of atoms; trapping - 33.20.Tp Vibrational analysis - 33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors