异核双原子和三原子分子在红外强激光场中的电离抑制

Ionization is the fundamental process in interaction of atoms/molecules with femtosecond strong laser fields. Comparing to atoms, molecules exhibit peculiar behaviors in strong-field ionization because of their diverse geometric structures, molecular electronic orbitals as well as extra nuclear degrees of freedom. In this study, we investigate strong field single and double ionization of carbon monoxide (CO) and carbon dioxide (CO₂) in linearly polarized 50-fs, 800-nm laser fields with peak intensity in the range of 2×10¹³ W/cm² to 2×10¹⁴ W/cm² using time-of-flight mass spectrometer. By comparing the ionization yields with that of the companion atom krypton (Kr), which has similar ionization potential to the molecules, we investigate the effect of molecular electronic orbitals on the strong-field ionization. The results show that comparing to Kr, no significant suppression is observed in single ionization of both molecules and in non-sequential double ionization (NSDI) of CO, while the NSDI probability of CO₂ is strongly suppressed. Based on our results and previous studies on homonuclear diatomic molecules (N₂ and O₂), the mechanism of different suppression effect is discussed. It is indicated that the different structure of the highest occupied molecular orbitals of CO and CO₂ leads to distinct behaviors in two-center interference by the electronic wave-packet and angular distributions of the ionized electrons, resulting in different suppression effect in strong-field ionization.     

铝原子团簇Al5、Al5-和Al5+稳定结构的密度泛函理论研究

采用密度泛函理论的四种方法 :杂化密度泛函B3LYP与B3PW 91、Perdew Wang91交换与相关泛函WP91PW91、局域自旋密度近似SVWN ,研究了Al5、Al5-和Al5+ 团簇的多种可能结构 ,找到了它们稳定的结构与自旋态 ,与已有的理论结果作了比较 ,并计算了Al5-的绝热与垂直电子离解能、Al5的绝热与垂直电离势 ,同有关的实验数据比较 ,符合较好 .同时对四种密度泛函方法的计算结果作了一些比较与讨论     

速率系数和亚稳态对氧的离化平衡和辐射损失的影响

本文依照定态日冕模型,采用不同速率系数的组合,计算氧的离化平衡和辐射损失。考虑了氧的三个砭稳态:类He离子OⅦ_(is2s~3)S,类Be离子OV_(1s~22s_2P~3)P,类B离子OⅣ_(1s~22s2P~2~4)P。计算亚稳态粒子占有数与基态粒子占有数之比随电子温度的变化。文中给出不同情况下,速率系数和亚稳态对氧的离化平衡和辐射能量损失的影响。     

The optimum pumping power for optically pumped FIR lasers

The relations between the output power of optically pumped FIR laser and the pumping power were studied theoretically by solving the density matrix equation of four-level system by means of the matrix signal flow graph method. The output power density of FIR laser was calculated by iteration method. A set of curves of output FIR power density against pumping power has been obtained. It has found that every of each curve has a maximum point of which the position is different for different pumping detuning. According the these results we predicted that there would exist an optimum pumping power density for an optically pumped FIR laser with certain pumping detuning. This theoretical results would help us to design the optically pumped FIR lasers.     

钾原子激光共振电离研究

用Ｎｄ：ＹＡＧ及其泵浦的染料激光进行钾原子三步共振电离研究。求解了非饱和共振过程速率方程，计算出基态和激发态的共振吸收截面；给出电离效率分别与各激发速率、电离速率以及作用时间的变化关系；得出饱和激发电离的流量条件和通量条件，并进行了讨论。     

Second ionization of carbonic acid in NaCl media to 250°C

The equilibrium quotients for the first ionization of aqueous carbon dioxide were previously determined at this laboratory. A similar potentiometric technique has now been employed to determine the second ionization quotients in NaCl media to 5m and from 50 to 250°C. The results have been combined with selected information in the literature and modeled to derive thermodynamic parameters including equilibrium constants, activity coefficient quotients, changes in enthalpies and changes in heat capacity along the saturation pressure curve. Approximate values for pressure coefficients were obtained to permit the short extrapolations from experimental conditions to the saturation pressure condition. The results demonstrate that log K₂/K_w, when plotted vs. 1/T, gives nearly a straight line as has been observed for a number of other such processes. This provides the best means of extrapolation beyond the temperature of the measurements. The results have been applied to an examination of the solubility of calcite (calcium carbonate) as a function of hydrogen ion molality (in a given NaCl medium) for the condition where the calcium ion molality equals the total carbonate molality (in all forms).On leave from Furman University, Greenville, SC     

O KVV Auger emission versus resonant photoemission at the O K edge of high-Tc superconductors

Photoelectron spectroscopy results on single crystals of the superconductors Bi₂Sr₂CaCu₂O₈,Bi₂Sr₂CuO₆, Ba_0.6K_0.4BiO₃ and the semiconductor Ba_0.9K_0.1BiO₃ are reported for the photon energy region around the O K absorption threshold. The development of the O-KVV Auger structure has been carefully monitored as a function of photon energy. A non-monotonic behavior displaying a feature at a constant binding energy of about 14 eV was found for Bi₂Sr₂CaCu₂O₈ and Bi₂Sr₂CuO₆ in a narrow photon energy region of 1 eV at the main edge of the O K absorption spectrum around 530 eV. The corresponding enhancement, connected with the autoionization of O 2p states, is absent in Ba_1−xK_xBiO ₃ in contrast to Bi₂Sr₂CaCu₂O₈ and Bi₂Sr₂CuO₆. The resonant enhancement is more pronounced for Bi₂Sr₂CuO₆ as compared to Bi₂Sr₂CaCu₂O₈, which can be explained by a lower charge carrier concentration in the former case, leading to a more localized nature of intermediate O 2p states. The model parameters Cu d–d and O p–p Coulomb interactions and the charge transfer energy Δ are estimated from the experiments.