异核Na(3P)+Cs(6P)系统的碰撞能量合并

置于同一池中的钠原子和铯原子,分别被连续染料激光器和铯光谱灯激发到Na(3P),Cs(6P),Na(3P)原子密度由吸收等效宽度技术来测定。利用调制技术,分离出了由异核碰撞产生的荧光光谱。观察到了Na(3P)和Cs(6P)间的碰撞能量合并现象,并测定了其碰撞截面。 关键词：     

Na(3P)+Na(3P)→Na(4F)+Na(3S)碰撞激发能量转移截面

利用激光(调离NaD_2线±20GHz)激发钠蒸汽,测量Na(3P)+Na(3P)→Na(4F)+Na(3S)的碰撞激发转移截面。因4F→3D的荧光位于红外(1.84μm),故检测3~2D_(3/2)→3~2P_(1/2)(818.3nm)和3~2D→3~2P_(3/2)(819.5nm)级联荧光信号。通过测量激光频率的Rayleigh散射光,直接D_2线荧光和敏化D_1线荧光分布,确定了钠原子密度,定出了有效辐射俘获衰变率Γ_(D_1)~e,Γ_(D_2)~e。结合激光功率吸收率的测量得到了Na(3P)的密度,从而给出转移截面σ(4F)=37A~2(±33％)。与其他作者的实验结果和理论值作了比较,进行了讨论。     

激发态钠原子间的碰撞能量合并

对钠蒸气中的碰撞能量合并过程Na(3P_J)+Na(3P_J′)→Na(nL_J″)+Na(3S_1/2)进行了实验研究．在低钠原子密度条件下，用激光将原子分别激发到3P_1/2或3P_3/2态，测量从nL_J″态发出的荧光强度比和Na(3P_3/2)与Na(3P_1/2)的密度比，给出了J′=J=1/2或3/2，nL_J″=4D_3/2，4D_5/2,4F_5/2，4F_7/2，5S_1/2的速率系数对打的比值、当销原子密度足够高时，3P态以统计比率布居，得到了k_(nLJ″)(1/2,3/2)对k_5S(3/2,3/2)的比值． 关键词：     

Cs(8D,9D)+Na(3S)碰撞激发转移过程

此文报道异核Cs(8D,9D)+Na(3S)→Cs(6P)+Na(3P)的碰撞能量转移过程.两步激发Cs原子到9D3/2(8D3/2)态.应用双调制技术探测Na(3PJ)原子发射的荧光,基态Na原子密度用光学吸收方法测量.得到了REP率系数,讨论了其它过程对率系数的影响.     

中低能非全裸C离子与He原子的碰撞研究

采用反冲离子飞行时间-散射离子位置灵敏符合测量技术，测量了能量范围在0.7v₀—4.4v₀(v₀为玻尔速度)的碳离子C^q+(q=1—4)与He原子碰撞过程不同出射道靶原子的双电离与单电离截面比R，包括入射离子不损失电子(直接电离)的出射道(R_q,q),入射离子俘获一个电子的出射道(R_q,q-1)和入射离子损失一个电子的出射道(R_q,q+1)，并研究了R随入射C离子的能量及电荷态的变化关系.实验表明，对给定电荷态的入射离子，靶原子的双电离与单电离截面比R与出射道有很强的依赖关系，即R_q,q<R_q,q+1<R_q,q-1.直接电离出射道截面比R_q,q与入射离子电荷态几乎无关，而入射离子俘获一个电子的出射道和损失一个电子的出射道靶原子双电离与单电离截面比R_q,q-1和R_q,q+1却与入射离子电荷态有很强的关系.采用原子极化理论和电子屏蔽与反屏蔽作用对实验结果进行了解释. 关键词： 离子-原子碰撞 电离 截面比     

含温有界原子模型下电子与离子碰撞激发和电离截面的理论研究

采用扭曲波玻恩交换近似方法，在自由原子模型下计算了电子与离子碰撞激发、电离截面，计算值与实验一致；在含温有界平均原子模型下，系统研究了不同温度、密度等离子体中离子的电子碰撞直接电离截面，发现由于温度、密度效应导致离子的能级漂移，引起等离子体中离子的碰撞电离截面比自由原子情形发生较大变化. 关键词： 平均原子模型 扭曲波波恩交换近似 电离截面     

Na(4D)+Na(3S)Na(4F)+Na(3S)碰撞能量转移截面

利用双光子吸收,将Na(3S)原子激发到4D态,测量了Na(4D)+Na(3S)Na(4F)+Na(3S)碰撞能量转移截面,因为直接由4F→3D的荧光不能探测,所以检测3D→3P级联荧光讯号。结合基态钠原子密度的测量,给出了截面值σ_4D→4F=1.3 x 10~(-14)±28％(cm~2)。     

C3+与Ne碰撞过程纯电离绝对截面的测量和研究

介绍了离子-原子碰撞过程中双微分绝对截面的计算方法.利用符合技术测量了中能区C³⁺+Ne碰撞系统的纯电离微分绝对截面. 将实验结果与多体经典蒙特卡罗方法计算结果进行对比后发现，纯电离截面随入射能量变化的趋势基本一致，对理论与实验产生差异的原因作了分析. 对多重电离的电离机制分析表明：高价态的反冲离子主要来自于俄歇贡献；随着入射能量的升高，电子-电子间的库仑作用也逐渐显现. 此实验方法可以用于相同实验装置上的各种反应出射道的绝对截面测量，入射离子种类及入射离子能量范围将得到拓展. 关键词： 离子-原子碰撞 绝对截面 纯电离     

用共振激发延迟电离方法测定原子激发态的光电离截面

用两束脉冲激光,一束使原子共振激发,另一束使激发态原子电离,当电离光脉冲能量约达1J/cm~2时,可使电离饱和.测量被电离原子数的相对大小与电离光脉冲能量之间的函数关系,可以方便地得出原子激发态的光电离截面.延迟电离光至激发光脉冲结束后到达作用区,可以修正激发光对电离的贡献,并避免电离光引起的Stark位移对共振激发的影响.应用共振激发延迟电离方法测定了Cs原子7~2P_(3/2)态的光(λ=5320(?))电离截面,测量值σ_I=6.5×10~(-18)cm~2与Manson的计算值非常接近.     

钠原子的饱和三步共振光离化

本文报道了用一个火花隙同时能发两台独立调谐的染料激光器(复合腔式、闪光灯泵浦)实现对钠原子(3S-3P-4D)三步共振饱和光电离,并对饱和跃迁情况下的系统速率方程进行了近似的解析解,与实验测得的电离曲线很好地符合,同时测量了电离激光束波长为5890A时的4D态电离截面,σ_(4D)=(1.2±0.4)×10~(-18)cm~2,并进行了电离截面的理论估计,与实验值较好地符合。     

Electron spectrometry study of associative and penning ionization in laser excited sodium vapor

The first observation, by electron spectrometry, is reported in laser-excited sodium vapor of the primary low energy electrons produced by associative ionization and by Penning ionization of sodium atoms in highly excited n1 states. The sequential heating of these primary electrons has been observed in 1, 2 or 3 superelastic collisions with Na(3p) atoms. The variation of associative ionization was measured as a function of the excited state density by using inner-shell photoionization produced by synchrotron radiation. Finally, an associative ionization cross section of 3.8 X 10^-17 cm² and a Penning ionization cross section for the 5s state of 1.1 X 10^-12 cm² were found (within 50% uncertainty) for an oven temperature of 520 K.     

Formation of higher-order fullerene dianions in collisions with Na atoms

We have measured electron capture cross sections in collisions between higher order fullerene anions C_n ^- (n=76, 78, 82, 84, 86, 90 and 96) and Na atoms. The ions were produced in an electrospray ion source (ESI) and accelerated to an energy of 50 keV. The measured cross section for dianion formation is three times larger for C₉₆ than that for C₆₀. The latter cross section was earlier found to be 36 ?². The dramatic increase of the cross section with fullerene size is explained by means of the curve crossing model for electron transfer.     

Ionization function of magnesium for electron impact

Ionization cross sections for electron impact are measured with crossed beams of Mg atoms and pulsed electrons. Total numbers of particles are determined by the light emission of excited atoms. The ionization cross section obtained for electron energies from 7 eV to 60 eV has its maximum valueq _i (max)=7.8 · 10^?16 cm² at 12 eV electron energy.     

Doubly charged clusters - neutral atom charge transfer: the role of the Coulombic repulsion

We have studied experimentally the collisional charge transfer between a neutral atom and a multicharged metal-atom cluster. The charge transfer cross section measured for Na ₃₁ ^{+ +} + Cs is in the range of 400 ?². The time-of-flight mass analysis of the singly charged collision products demonstrates that an energy of about 0.5 eV is deposited in the cluster fragment during the charge transfer collision. This effect can be interpreted as a charge transfer to an excited state of the metal cluster. The measured cross section for Na ₃₁ ^{+ +} + Cs is larger than the one for Na ₃₁ ⁺ + Cs collisions. This difference between these two systems is due to the existence, for the first one, of a Coulombic repulsion term in the collision output channel. Received 24 October 2000     

The photoproton reaction of 25Mg

The proton yields from the ²⁵Mg(e, p) reaction have been measured for E_p > 3 MeV, at θ = 90°, using an enriched ²⁵Mg sample in the electron energy range 15–28 MeV. Partial photoproton cross sections to the ground and excited states in ²⁴Na have been deduced and a lower limit is placed on the ²⁵Mg(γ, np) cross section. The derived photoproton cross section combined with existing photoneutron data allows the ²⁵Mg absorption cross section to be estimated. Configuration splitting of the ²⁵Mg GDR is confirmed, and the effects of isospin splitting are considered.     

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.     

Stimulated photon echo study of Na(32S12)-CO velocity-changing collisions

Using the recently developed single-state stimulated photon echo technique, we have studied the velocity changes experienced by ground-state Na atoms in collisions with carbon monoxide molecules. We find that the ground-state Na atoms have a total cross section of ≈420 Ų for velocity-changing collisions with CO, and that they experience an average velocity change of ≈600 cm/s. A scattering kernel of exponential form is shown to be consistent with our results. We discuss the essential features of the estimated photon echo technique.     

A new optical method of measuring electron impact excitation cross section of atoms: Cross section of the metastable 6s6p P0 level of Hg

We report a new method that is potentially applicable to the measurement of electron impact excitation cross section of any atoms. Measurement of the cross section of the metastable 6s6p ³P₀ level of mercury is conducted to demonstrate the method, which involves using cavity ringdown spectroscopy to determine the absolute number density of mercury atoms in the 6s6p ³P₀ energy level. The measured cross section is 1.7×¹⁰−17 cm² and in agreement with the literature values. Compared with the optical methods that have been used during the last three decades, this new approach not only serves as an alternative optical method, but also is applicable to the atoms under both high and low pressure conditions.     

Quenching of vacuum ultraviolet fluorescence emission from electron beam excited quasi-molecular xenon

A pressure dependent quenching of the VUV broad-band fluorescence (bandwidth 15 nm centred at λ 173 nm) from high pressure xenon has been measured for pressures from 25 to 215 p.s.i. The experimental results can be explained by collisional de-excitation of the excited Xe₂ molecules by Xe atoms. A quenching cross section of ≈ 10^-17 cm², and molecular radiative lifetime of 16 nsec have been derived. The implications for the design of VUV molecular xenon lasers are discussed.     

Evolution of molecular states studied in collisions of ions with laser excited atoms by a crossed beam experiment

Differential scattering cross sections in the energy rangeE _CM=25–50 eV have been measured in a crossed beam machine for the scattering of Na⁺ by laser excited Na(3² P _3/2). The superelastically scattered ions resulting from the collisional deexcitation process 3² P _3/2-² S _1/2 are sharply peaked at a constant reduced scattering angle of 180eV degrees. Through the choice of either linearly or circularly polarized light, one can selectively excite the magnetic sublevels of the Na atoms. This ability to align or orient the Na^* allows us to discuss in considerable detail both the transition from the space-fixed (atomic) to the body-fixed (molecular) system and the dynamics in the merging region of the two frames. We find that the symmetry axis of the excited electron charge cloud is locked to the internuclear axis and hence to the body-fixed reference frame at an internuclear separation of about 35 a.u. A pronounced asymmetry of the scattering from atoms excited with LHC or RHC polarized light is discussed in terms of simple models.