反冲原子对低速离子轰击Si表面时电子发射产额的影响

在兰州重离子加速器国家实验室电子回旋共振离子源高电荷态原子物理实验平台上,用低能(0.75keV/u≤EP/MP≤10.5keV/u,即3.8×105m/s≤vP≤1.42×106m/s)He2+,O2+和Ne2+离子束正入射到自清洁Si表面时二次电子发射产额的实验结果.结果表明电子发射产额γ近似正比于入射离子动能EP/MP.在相同动能下,γ(O)γ(Ne)γ(He),对于原子序数ZP比较大的O2+和Ne2+离子,ZP大者反而γ小,这与较高入射能量时的结果截然不同.通过计算不同入射能量下入射离子的阻止能损S,发现反冲原子对激发二次电子的作用随入射离子能量的降低显著增大,这正是导致在较低能量范围内二次电子发射产额与较高入射能量时存在差异的主要原因.     

Si5++He相互作用时双活跃电子势能的计算

利用附加电子转移因子和开关函数的半经典近似和量子分子轨道方法,在0.3～3.0 KeV能区和2.0～20.0(a.u.)核间距的条件下,对Si5+离子与He原子相互作用过程中5个singlet 态和5个triplet态的双电子捕获势能进行了理论计算.通过参数优化,在比较了基通道电子转移势能和实验值之后,研究了主通道的电子转移势能.其结果说明了这一动力学过程中的避交叉(avoided crossings)性质,给出了双电子容易被捕获的不同核间距离点.     

He2+离子与H原子的重粒子碰撞电离过程

利用初态程函近似的连续扭曲波方法研究了He²⁺离子与Ｈ原子的碰撞电离过程. 计 算得到了入射离子能量从30keV/u到2000keV/u的碰撞电离总截面、随电离电子能量和角度变 化的一阶和二阶微分散射截面，及随入射离子能量变化的电离电子平均能量.计算的总电离 截面与其他理论和实验结果进行了比较，在入射离子能量大于100keV／u的能区，计算结果 与实验符合得很好；在较低的能区，各种理论结果之间有较大差别，计算结果比实验约小50 ％.利用计算的二阶微分散射截面讨论了软碰撞、电子俘获到入射离子连续态、两体相遇碰 撞等碰撞电离机理. 关键词： 重粒子碰撞电离 初态程函近似 总截面 一阶和二阶微分散射截面     

HeH2+分子谐波辐射的空间分布

理论研究了HeH2+分子发射高次谐波的空间分布情况。结果表明：分子谐波发射主要集中在He核和H核附近。当核间距离较小时,He核辐射谐波强度要比H核辐射谐波强度高2~3个数量级。当核间距离较大时,He核辐射谐波强度要比H核辐射谐波强度高4~5个数量级。当空间非均匀激光场引入后,谐波截止能量得到延伸,并且,随着空间非均匀激光场位置由负向到正向移动(-100 a.u.到100 a.u.),谐波截止得到进一步延伸。但是He核辐射谐波强度依然大于H核。最后,通过叠加谐波可获得脉宽在60 as的超短脉冲。     

HeH2+分子谐波辐射的空间分布

理论研究了HeH2+分子发射高次谐波的空间分布情况。结果表明：分子谐波发射主要集中在He核和H核附近。当核间距离较小时,He核辐射谐波强度要比H核辐射谐波强度高2~3个数量级。当核间距离较大时,He核辐射谐波强度要比H核辐射谐波强度高4~5个数量级。当空间非均匀激光场引入后,谐波截止能量得到延伸,并且,随着空间非均匀激光场位置由负向到正向移动(-100 a.u.到100 a.u.),谐波截止得到进一步延伸。但是He核辐射谐波强度依然大于H核。最后,通过叠加谐波可获得脉宽在60 as的超短脉冲。     

O3+与氦原子碰撞过程的CTMC计算

应用经典径迹蒙特卡罗方法研究了O3+离子与氦原子碰撞的各种反应过程.基于使用多个系统总能量U值,对初始电子的微正则分布进行了优化,使其更接近于量子力学的径向空间分布.作为检验,首先在独立电子模型近似下计算了He2+与氦原子碰撞的各种反应过程,通过与实验的比较,发现对氦原子靶,优化极大地提高了计算精度.计算了O3+与氦原子随入射离子能量变化的各种反应过程截面,特别是单电子丢失、双电子丢失的总截面,以及转移电离截面与单俘获截面的比值,并与实验进行了比较,发现单双电子丢失截面与实验符合得很好,但在大于200 keV/u的能区,转移电离截面与单俘获截面的比值与实验有较大的差距,这表明独立电子模型需要进一步改进.     

反应窗理论的适用性研究

基于低能离子与原子碰撞的分子库仑过垒模型，简要描述了与入射离子速度相关的反应窗理论.根据这一理论，计算了不同碰撞速度时O⁸⁺-H，Ar⁸⁺-H，Ar⁸⁺-He，Ne¹⁰⁺-He及Ar¹⁸⁺-He等碰撞体系单电子俘获过程的微分截面，还计算了碰撞速度为0.53 a.u.时¹⁵N⁷⁺-Ne碰撞体系单电子、双电子及三电子俘获过程的微分截面，并与他人的实验结果作了比较.研究发现，反应窗理论预言的末态电子分布与实验结果符合较好.理论和实验研究表明，随着碰撞速度的增加反应窗变宽；反应窗理论所预言的微分截面，当Q值较小时比实验结果偏大，当Q值较大时比实验结果偏小. 关键词： 反应窗理论 态选择微分截面 分子库仑过垒模型 离子与原子碰撞     

Li2基态结合能的MACQM计算

本文采用改进的排列通道量子力学方法(MACQM),对Li2基态势能曲线进行了计算,结果表明:在核间距R=5.05a0处,能量有极小值-14.88937a.u,由此得到Li2基态结合能为0.0333a.u,所得结果与实验值符合得很好.     

电子入射双电离He原子的理论研究

完成了高入射能(E05.6keV),低敲出能(E1=E2=10eV)情形下,电子入射双电离He原子五重微分截面(FDCS)的理论计算.计算中使用了三个电子在He+2离子场中的四体末态波函数.计算结果与其他理论结果进行比较发现:所得结果与最新的(e,3e)实验数据较好地一致.     

HeH~(2+)分子谐波辐射的空间分布

理论研究了HeH~(2+)分子发射高次谐波的空间分布情况.结果表明:分子谐波发射主要集中在He核和H核附近.当核间距离较小时,He核辐射谐波强度要比H核辐射谐波强度高2~3个数量级.当核间距离较大时,He核辐射谐波强度要比H核辐射谐波强度高4~5个数量级.当空间非均匀激光场引入后,谐波截止能量得到延伸,并且,随着空间非均匀激光场位置由负向到正向移动(-100 a.u.到100a.u.),谐波截止得到进一步延伸.但是He核辐射谐波强度依然大于H核.最后,通过叠加谐波可获得脉宽在60 as的超短脉冲.     

Formation Mechanism and Binding Energy for Icosahedral Central Structure of He1+3 Cluster

The formation mechanism for the icosahedral central structure of the He1 13 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 He 13 with respect to He 12He was calculated to be 1.4046 a.u. This means that the cluster of He 13 may be formed in an icosahedral central structure with strong binding energy.     

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 totalenergy curve is calculated by the method of a modified arrangement channel quantum mechanics (MACQM). The energyis a function of separation R between two nuclei at the center and an apex of the octahedral central structure. The resultof the calculation shows that the curve has a minimal energy -19.7296 a.u. At R = 2.40 α0. The binding energy of He7 with respect to He 6He was calculated to be 0.6437 a.u. This means that the cluster of He7 may be formed in thestable octahedral central structure with R = 2.40 α0.     

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.     

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.     

Formation Mechanism and Binding Energy for Equilateral Triangle Structure of He3+ Cluster

The formation mechanism for the equilateral triangle structure of the He3 cluster is proposed. The curveof the total energy versus the internuclear distance R for this structure has been calculated by the method of a modifiedarrangement channel quantum mechanics. The result shows that the curve has a minimal -7.81373 a.u at 1 = 1.55 a0.The binding energy of He3 with respect to He He He was calculated to be 0.1064 a.u. (about 2.89 eV). This meansthat the He3 cluster may be formed in the equilateral triangle structure stably by the interaction of He with two heliumatoms.     

Formation Mechanism and Binding Energy for Regular Tetrahedral Structure of Li4

The formation mechanism for the regular tetrahedral structure of Li4 cluster is proposed. The curve of the total energy versus the separation R between the two nuclei has been calculated by using the method of Gou＇s modified arrangement channel quantum mechanics （MACQM）. The result shows that the curve has a minimal energy of-29.8279 a.u. at R = 14.50 ao. When R approaches infinity the total energy of four lithium atoms has the value of-29.7121 a.u. So the binding energy of Li4 with respect to four lithium atoms is the difference of 0.1158 a.u.for the above two energy values. Therefore the binding energy per atom for Lh is 0.020 a.u., or 0.7878 eV, which is greater than the binding energy per atom of 0.453 eV for Li2, the binding energy per atom of 0.494 eV for Lia and the binding energy per atom of 0.632 eV for Li5 calculated previously by us. This means that the Li4 cluster may be formed stably in a regular tetrahedral structure of side length R = 14.50 ao with a greater binding energy.     

Formation Mechanism and Binding Energy for Regular Octahedral Structure of Li6 Cluster

The formation mechanism for the regular octahedral structure of Li₆ cluster is proposed. The curve of the total energy versus the separation R between any two neighboring nuclei has been calculated by using the method of Gou's modified arrangement channel quantum mechanics (MACQM). The result shows that the curve has a minimal energy of -44.736 89 a.u. at R = 5.07a₀. When R approaches infinity, the total energy of six lithium atoms has the value of -44.568 17 a.u. So the binding energy of Li₆ with respect to six lithium atoms is 0.1687 a.u. Therefore, the binding energy per atom for Li₆ is 0.028 12 a.u., or 0.7637 eV, which is greater than the binding energy per atom of 0.453 eV for Li₂ and the binding energy per atom of 0.494 eV for Li₃ calculated in our previous work. This means that the Li₆ cluster may be formed in a regular octahedral structure with a greater binding energy.     

The formation mechanism and the binding energy the body—centred regular tetrahedral structure of He5^＋

We propose the formation mechanism of the body-centred regular tetrahedral structure of the He5^ cluster,The total energy curve for this structure has been calculated by using a modified arrangement channel quantum mechanics method.The result shows that a minimal energy of -13.9106 a.u.occurs at a separation of 1.14a0 between the nucleus at the centre and nuclei at the apexes.Therefore we obtain the binding energy of 0.5202a .u.for this structure.This means that the He5^ cluster may be stable with a high binding energy in a body-centred regular tetrahedral structure.     

Li9团簇体心立方结构的形成机理和结合能

本文提出了Li9团簇体心立方结构的形成机理,并对此结构的总能量随中心原子到顶点原子间核间距R的变化用芶氏改进的排列通道量子力学方法(MACQM)进行了计算。结果显示曲线在R = 4.77 a0处有一极小值 -67.160922 a.u.,这表明Li9团簇的体心立方结构是可能稳定存在的。在R趋于无穷大时这9个锂原子的总能量为 -66.852240 a.u.,所以形成Li9的总结合能为0.308682 a.u.。因此Li9 团簇的原子平均结合能是0.034298 a.u.或0.933 eV,它大于我们过去计算的Li5团簇正四面体中心结构的原子平均结合能0.632 eV、Li7 团簇正八面体中心结构的原子平均结合能0.674 eV和Li13 团簇正二十面体中心结构的原子平均结合能0.810 eV。故在体心正多面体结构Lin (n= 5 ,7,9,13)中,Li9的体心立方结构有最大的原子平均结合能,这也许是碱金属晶体的晶胞取体心立方结构的一个原因。     

Formation Mechanism and Binding Energy for Body-Centred Regular Octahedral Structure of Li7 Cluster

The formation mechanism for the body-centred regular octahedral structure of Li7 cluster is proposed. The curve of the total energy versus the separation R between the nucleus at the centre and nuclei at the apexes for this structure of Li7 has been calculated by using the method of Gou＇s modified arrangement channel quantum mechanics （MACQM）. The result shows that the curve has a minimal energy of-52.169 73 a.u. at R = 5.06ao. When R approaches infinity, the total energy of seven lithium atoms has the value of-51.996 21 a.u. So the binding energy of Li7 with respect to seven lithium atoms is 0.173 52 a.u. Therefore the binding energy per atom for Li7 is 0.024 79 a.u. or 0.674 eV, which is greater than the binding energy per atom of 0.453 eV for Li2, the binding energy per atom of 0.494 eV for Li3 and the binding energy per atom of 0.632 eV for Li5 calculated previously by us. This means that the Li7 cluster may be formed stably in a body-centred regular octahedral structure with a greater binding energy.