Collision relaxation cross section of highly vibrationally excited molecules

Through quantum-beat spectroscopy collision relaxation of a high vibrational level of SO2 at 44 877.52 cm(-1) is characterized. This is a first measurement of collision relaxation for a single, highly excited vibrational level. The deduced relaxation cross section of this excited level by Ar is 216 A(2), 5 times the area of the hard sphere, and by an ambient temperature SO2 molecule is 969 A(2), almost 20 times the hard sphere. These cross sections indicate that relaxation collisions of highly vibrationally excited molecules have effective distances much longer than van der Waals radii and involve mechanisms qualitatively different from lower excitations.     

Electron impact cross sections of vibrationally and electronically excited molecules

It is well known that the electron impact cross sections for elastic and inelastic processes for the vibrationally and electronically excited molecules are predominantly different than those for molecules in the ground state. Collisions of low energy electrons with excited molecules play an important role in explaining the behavior of gas discharges in laser and plasma physics, in planetary atmospheres, stars, and interstellar medium and in plasmas widely used in the fabrication of microelectronics. This explains as to why there is a need for having validated sets of electron impact cross sections for different processes. This work reviews the subject of electron collisions with vibrationally and electronically excited molecules in a comprehensive way. The survey has been carried out for a few excited molecules such as H₂, D₂, T₂, HD, HT, DT, N₂, O₂, and CO₂.     

Autoionization cross section of potassium atom excited by electron impact

The autoionization cross section of potassium atoms excited by electron impact is measured in the energy range from the first autoionization threshold at 18.72 eV to 202 eV. The data are obtained by deter-mining the total intensity of electron spectra resulting from the decay of the 3p ⁵ n ₁ l ₁ n ₂ l ₂ autoionizing states. The cross section has two maxima, 1.8 × 10^?16 and 2.2 × 10^?16 cm², at 21 and 32 eV, respectively. The excitation dynamics of autoionization states suggests that the first maximum is associated with the resonance character of the near-threshold excitation. The second maximum, as well as the behavior of the cross section at energies above 50 eV, reflects the dynamics of electron excitation of quartet and doublet autoionizing states. The measured autoionization cross section is compared with known data for the total single ionization cross section of potassium atom by electron impact. The relative contribution of the autoionization cross section to the total single ionization cross section is found to reach 30% at 32 eV.     

Autoionization cross section of lithium atoms excited by electron impact

We measure the full autoionization cross section of lithium atoms excited by electrons in the energy range from the first autoionization threshold at 56.39 to 600 eV. Data are obtained by determining the total intensity of electron spectrum of autoionization states 1sn ₁ l ₁ n ₂ l ₂ detected at the “magic” observation angle of 54.7°. The cross section behavior is characterized by a sharp increase to a maximum value of 1.7 × 10⁻¹⁸ cm² in the energy interval of 56.4–60 eV and a subsequent monotonic drop to a value of 10⁻¹⁸ cm² at 600 eV. We have discovered a “thin” cross section structure that reflects the presence of strong resonances of Li⁻ ions in the near-threshold area of excitation of the lowest energy autoionization states (1s2s2)2S, (1s2s2p)⁴ P, 1s(2s2p ³ P)² P), and 1s(2s2p ¹ P)² P. We have established that the contribution of autoionization to the absolute cross section of single ionization of lithium atoms does not exceed 4%. We perform a comparative analysis of the data with analogous data for potassium and cesium atoms.     

He和D_2分子相互作用转动激发研究

用T .T(K .T .TangandJ .Peter.Toennies)势模型和公认精密度较高的密耦 (Close Coupling)近似方法计算了E =0 .1eV和E =0 .2eV时 ,0 0— 0 0弹性碰撞及 0 0— 0 2、0 0— 0 4、0 0— 0 6非弹性碰撞 ,得出D2 分子转动激发分波截面 ,并得到了原子与分子碰撞弹性分波截面和非弹性激发截面随量子数增加的变化规律。     

He-BH碰撞体系微分截面的理论计算

用公认精确的密耦近似方法计算了入射能量从25至150 meV时,He原子与基态BH分子碰撞的弹性微分截面、非弹性微分截面和总微分截面,进一步讨论了微分截面的变化趋势及特征.计算结果表明：He-BH碰撞体系的总微分截面具有原子与双原子分子散射的一般规律和特征;随着入射能量的增加,低转动激发态-态微分截面在大角区的散射振荡现象会更加明显. 关键词： He-BH复合物 相互作用势 密耦近似 微分截面     

He-NO碰撞体系微分截面的理论计算

首先用Huxley势函数形式拟合了在RCCSD(T)/aug-cc-pVTZ+bf理论水平下计算的He-NO相互作用能数据，获得了He原子与NO分子相互作用的各向异性势，然后采用密耦近似方法计算了He-NO碰撞体系的总微分截面、弹性微分截面和非弹性微分截面，并总结了微分散射截面的变化规律. 结果表明，拟合势不但表达形式简洁，而且较好地描述了He-NO系统相互作用的各向异性特征；利用碰撞体系分子间势的量子化学从头计算结果,可解决势能参数难以确定的问题，对进一步研究原子与分子碰撞机理有一定参考价值. 关键词： 各向异性势 势能参数 密耦近似 微分截面     

Ionization of long-lived highly excited atoms by collision with molecules. II

A theoretical treatment of the collisional ionization of a highly excited atom with a molecule is improved by use of the exact form factor of the hydrogen atom in highly excited states. The present treatment is still based on the previously proposed mechanism in which the Rydberg electron is ionized by gain of energy from rotational de-excitation of the molecule in a rotationally excited state. Closer comparison of experiment with theory is made for symmetric- as well as asymmetric-top molecules.     

Dendrimer molecules with record large two-photon absorption cross section

We report what is to our knowledge a record high value for an intrinsic two-photon absorption (TPA) cross section, sigma(2) = 11 x 10(-47)> cm>(4)> s photon(-1) molecule(-1), measured with femtosecond pulses in a new dendrimer molecule comprising 29 repeat units of 4, 4(?)-bis(diphenylamino)stilbene chromophore. We measure the dependence of TPA on excitation wavelength in three consecutive generations of the dendrimer and show that the maximum sigma(2) value increases faster than the total number of stilbene chromophores. This result indicates that it is possible to obtain even larger sigma(2) values in higher generations of this dendrimer family.     

Isospin effect of the in-medium nucleon-nucleon cross section in excited nuclear reactions

Using relativistic mean field theory, the neutron and the proton density distribution of 56Ni nuclei could be obtained in the ground state and the excited state. Based on the framework of the quantum molecular dynamics model, the 56Ni nuclei have been simulated in ground state and in the neutron or proton excited state. We then used the three different states of 56Ni to collide with the 56Ni in the ground state. To discuss the evolution of the nuclear stopping in different reactions, two kinds of different excited nuclear reactions were studied at different reaction energies and at different impact parameters. Studies have shown that the nuclear stopping of an excited nuclear reaction is sensitive to the isospin-dependent in-medium nucleon-nucleon cross section, compared with the response value of the ground state nuclear reaction. So, it is better for the excited nuclei to extract the isospin dependence of nucleon-nucleon cross section information.     

Isospin effect of the in-medium nucleon-nucleon cross section in excited nuclear reactions

Using relativistic mean field theory, the neutron and the proton density distribution of ⁵⁶Ni nuclei could be obtained in the ground state and the excited state. Based on the framework of the quantum molecular dynamics model, the ⁵⁶Ni nuclei have been simulated in ground state and in the neutron or proton excited state. We then used the three different states of ⁵⁶Ni to collide with the ⁵⁶Ni in the ground state. To discuss the evolution of the nuclear stopping in different reactions, two kinds of different excited nuclear reactions were studied at different reaction energies and at different impact parameters. Studies have shown that the nuclear stopping of an excited nuclear reaction is sensitive to the isospin-dependent in-medium nucleon-nucleon cross section, compared with the response value of the ground state nuclear reaction. So, it is better for the excited nuclei to extract the isospin dependence of nucleon-nucleon cross section information.     

He同位素对He-NO碰撞体系微分截面的影响

用密耦近似方法计算了同位素He原子与NO分子碰撞体系的总微分截面、弹性微分截面和非弹性微分截面,总结了同位素He原子对He-NO碰撞体系微分截面的影响. 计算结果表明：在同一入射能量下,随着入射同位素He原子质量增加,总微分截面在0°时的角分布逐渐增大;同位素He原子与NO分子碰撞发生的彩虹现象越明显. 同时,体系约化质量增加的效应大于相对碰撞速度减小的效应,使散射振荡间隔逐渐减小. 关键词： He-NO 密耦近似 微分截面 同位素效应     

Donor-acceptor pair capture cross section for highly excited electrons in polar semiconductors

The capture cross section σ (R) for Donor-Acceptor Pairs (DAPs) with pair separation distance R is improved for the case of hot carriers by taking into account the LO-phonon interaction so that an energy dependend cross section σ(E_k, R) results. This latter process, which is of importance for a non-equilibrium carrier distribution, yields a preferential occupation of close DAPs thus provoking a blue shift and a deformation of the main emission band if compared with line profiles where only thermalized carriers are involved.     

Inelastic collision term in dilute magnetic alloys

The collision term derived by Kohn and Luttinger [1] to describe elastic scattering to third order in the potential is generalized to include inelastic processes for a system of conduction electrons interacting with localized spins. This result is obtained by using the Kadanoff and Baym [6] derivation of the Boltzmann equation.     

Inelastic light scattering in highly excited GaAs

The coupled plasmon-LO-phonon and single-particle excitations of a photocreated electron-hole plasma in high purity GaAs are studied by means of Raman scattering measurements. The experimental results are described by the random-phase approximation with respect to the multicomponent character of optical plasma. From single-particle spectra the plasma distribution function and drift velocities up to 10⁷ cm/s have been determined. Using the coupled modes as probe for the plasma density the temperature dependence of the recombination in the EHP is studied.     

铝原子激发态近阈限光电离截面测量

本文利用激光烧蚀、激光泵浦-探测、共振增强多光子电离和飞行时间质谱相结合的实验技术,根据离子产额和电离激光能量的关系,获取铝原子激发态的光电离截面;并研究了光电离截面与电离富余能的依赖关系.电离富余能0-2.98 eV内光电离截面值范围为15.6±1.7 Mb-2.3±0.9 Mb,激发态的寿命为17.6±1.8,16.9±1.7ns.在光电离截面的测量中,总的均方根误差上限约为17%.     

铝原子激发态近阈限光电离截面测量

本文利用激光烧蚀、激光泵浦-探测、共振增强多光子电离和飞行时间质谱相结合的实验技术,根据离子产额和电离激光能量的关系,获取铝原子激发态的光电离截面;并研究了光电离截面与电离富余能的依赖关系.电离富余能0-2.98 e V内光电离截面值范围为15.6±1.7 Mb-2.3±0.9 Mb,激发态的寿命为17.6±1.8,16.9±1.7 ns.在光电离截面的测量中,总的均方根误差上限约为17%.     

电子与离子碰撞过程中辐射复合截面的相对论理论研究

在相对论理论框架下,研究了自由电子与离子碰撞的辐射复合过程.在分析影响单电子体系(类H+离子及碱金属离子)辐射复合截面主要因素的基础上,总结出了辐射复合截面在不同情况下的变化规律.