The Limit of Rotational Energy Transfer in Atom-Diatom Collision and the Hard Ellipsoid Potential Model

The limit of rotational energy transfer in atom-diatomic systems due to inelastic collision was investigated over the wide range of collision energy, reduced mass and potential parameters of F2-He system. The IICS （integral inelastic cross-sections） is obtained by the IOSAM （infinite order sudden approximation method） and predicted by PG （power-gap） law in the variation of cross-sections. The investigation provided that the classical limit of angular momentum transfer is given by hard ellipsoid potential is meaningful even the cross-sections computed on the real potential, provided the classical turning point on the surface of soft potential is assumed as hard potential surface.

Loss of cold atoms due to collisions with residual gases in free flight in a magneto-optical trap

The loss rate of cold atoms in a trap due to residual gas collisions differs from that in a free state after the cold atoms are released from the trap. In this paper, the loss rate in a cold rubidium-87 atom cloud was measured in a magneto-optical trap （MOT） and during its free flight. The residual gas pressure was analyzed by a residual gas analyzer, and the pressure distribution in a vacuum chamber was numerically calculated by the angular coefficient method. The decay factor, which describes the decay behavior of cold atoms due to residual gas collisions during a free flight, was calculated. It was found that the decay factor agrees well with theoretical predictions under various vacuum conditions.

Electric-field-modified Feshbach resonances in ultracold atom–molecule collision

We present a detailed analysis of near zero-energy Feshbach resonances in ultracold collisions of atom and molecule,taking the He–PH system as an example, subject to superimposed electric and magnetic static fields. We find that the electric field can induce Feshbach resonance which cannot occur when only a magnetic field is applied, through couplings of the adjacent rotational states of different parities. We show that the electric field can shift the position of the magnetic Feshbach resonance, and change the amplitude of resonance significantly. Finally, we demonstrate that, for narrow magnetic Feshbach resonance as in most cases of ultracold atom–molecule collision, the electric field may be used to modulate the resonance, because the width of resonance in electric field scale is relatively larger than that in magnetic field scale.

Collision Characteristics between Ultracold Cesium <i>nP</i>Rydberg Atoms

We investigate the effect of van der Waals interactions and dipole-dipole interactions on collisional loss rate coefficients of Cs Rydberg nP states, and in detail analyze the variation of collisional loss coefficients under the initial Rydberg atomic velocity and van der Waals interactions. We obtain the total collisional loss coefficients for different nP states, and provide the possible ionization mechanism for the results of experimental observation using our analysis model.

Single-and-double electron loss of O^(2+) in collisions with argon and helium

This paper reports that the ratios of double to single electron loss cross-section （R） of O^2＋ in collision with Ar and He at the velocity of 1 -4 vo（vo is the Bohr velocity） have been obtained by the coincidence technique. The trend of R - V in the experiment indicates that the effective charge varies with injected velocity. The effective charge can be obtained by the n-body classical trajectory Monte Carlo method, which is interpreted by the molecular Coulomb over barrier model.

Investigation of the transfer ionization process in collisions of partially stripped ions on He

In this paper a projectile ion-recoil ion coincidence technique is used to investigate the transfer ionization processes in collisions of 0.22-6.30 MeV Cq＋ ions and 0.25-6.35 MeV 0q＋ ions （q=1, 2, 3, 4） with the He atom separately. The cross section ratio f of transfer ionization to single electron transfer is measured, and the dependence of f on both charge state q and energy E of the projectiles is investigated. The electron-structure and the mechanisms leading to transfer ionization affect the dependence of f on q and E. Our measurements, along with other data published previously, suggest a similar dependence of f on charge state and energy of projectile for partially stripped ions over a large energy range. The maximum value of f is approximately 0.17q^0.60; the energy corresponding to maximum f is about 160q^0.60 keV/u.

Elastic scattering of two H(~2S_g) and N(~4S_u) atoms at low temperatures and accurate spectroscopic parameters of NH (X^3Σ^-) radical

This paper reports that the interaction potential for the X3Z- state of NH radical is constructed at the CCSD（T）/ cc-PV6Z level of theory. Using this potential, this paper calculates the spectroscopic parameters （De, Re, ωe, ωeχe, αe and Be） and their values are of 3.578eV, 0.10368nm, 3286.833cm^-1, 78.433cm^-1, 0.6469cm^-1 and 16.6735cm^-1 respectively, which are in excellent agreement with the experiments. Then the total of 14 vibrational states has been found when J=0 by solving the radial Schrodinger equation of nuclear motion. For each vibrational state, the vibrational manifolds are reported for the first time. And last, the total cross sections, s-wave, p-wave and d-wave cross sections are computed for the elastic collisions between two ground-state atoms （hydrogen and nitrogen） at low temperatures. It finds that the total elastic cross sections are dominated by s-wave scattering when the collision energy is below 10^-6a.u. The pronounced shape resonance is found at energy of 6.1 × 10^-6a.u. Calculations have shown that the shape resonance comes from the p-wave contributions.

Temperature and number evolution of cold cesium atoms inside a wall-coated glass cell

We report an experimental study on the temperature and number evolution of cold cesium atoms diffusively cooled inside a wall-coated glass cell by measuring the absorption profile of the 62S1/2 （F = 4） →62P3/2（F= 5） transition line with a weak probe laser in the evolution process. We found that the temperature of the cold atoms first gradually decreases from 16 mK to 9 mK, and then rapidly increases. The number of cold atoms first declines slowly from 2.1 × 109 to 3.7×108 and then falls drastically. A theoretical model for the number evolution is built and includes the instantaneous temperature of the cold atoms and a fraction p, which represents the part of cold cesium atoms elastically reflected by the coated cell wall. The theory is overall in good agreement with the experimental result, and a nonzero value is obtained for the fraction p, which indicates that the cold cesium atoms are not all heated to the ambient temperature by a single collision with the coated cell wall. These results can provide helpful insight for precision measurements based on diffuse laser cooling.

Total cross sections for electrons scattering from simple molecules containing the larger atom sulfur at 30-5000eV

A complex optical model potential modified by the concept of bonded atom, which takes into consideration the overlapping effect of electron clouds, is employed to calculate the total cross sections for electrons scattering from simple molecules （SO2, H2S, OCS, CS2 and SO3） containing the larger atom, sulfur, at 30-5000eV by using the additivity rule model at Hartree-Fock level. The quantitative molecular total cross section results are compared with those obtained in experiments and other calculations wherever available, and good agreement is obtained. It is shown that the additivity rule model together with the complex optical model potential modified by the concept of bonded atom can give the results closer to the experiments than the one unmodified by it. So, the introduction of bonded-atom concept in complex optical model potential betters the accuracy of the total cross section calculations of electrons from the molecules containing the larger atom, sulfur.

A Correlation Potential Method for Electron Scattering Total Cross Section Calculations on Several Diatomic and Polyatomic Molecules over Energy Range 10～5000eV

A complex optical model potential correlated by the concept of bonded atom, which considers the overlapping effect of electron clouds between two atoms in a molecule, is firstly employed to calculate the total cross sections for electron scattering on several molecules (NH3, H2O, CH4, CO, N2, O2, and C2H4) over the energy range 10 ～ 5000 eV using the additivity rule model at Hartree-Fock level. The difference between the bonded atom and the free one in states is that the overlapping effect of electron clouds of bonded atoms in a molecule is considered. The quantitative total cross sections are compared with the experimental data and with the other calculations wherever available and good agreement is obtained over the energy range 10 ～ 5000 eV. It is shown that the correlated calculations are much closer to the available experimental data than the uncorrelated ones at lower energies, especially below 500 eV. Therefore,considering the overlapping effect of electron clouds in the complex optical model potential could be helpful for the better accuracy of the total cross section calculations of electron scattering from molecules.

Numerical Investigation of the Tri-Atomic Ions Formation during Laser Ionization Based on Resonance Saturation

We present a theoretical investigation of plasma generation in sodium vapor induced by laser radiation tuned to the first resonance line (3S-3P) at λ = 589 ns. A set of rate equations that describe the rate of change of the ground and excited states population as well as the temporal variation of the electron energy distribution function (EEDF), beside the formed atomic ion Na+, molecular ion ?and tri-atomic ions are solved numerically. The calculations are carried out at different laser energy and different sodium atomic vapor densities under the experimental conditions of Tapalian and Smith (1993) to test the existence of the formed tri-atomic ions. The numerical calculations of the electron energy distribution function (EEDF) show that a deviation from the Maxwellian distribution due to the super elastic collisions effect. In addition to the competition between associative ionization (3P-3P), associative ionization (3P-3D) and Molnar-Horn- beck ionization processes for producing , the calculations have also shown that the atomic ions Na+ are formed through the Penning ionization and photoionization processes. These results are found to be consistent with the experimental observations.

H2诱导Cs（6DJ→Cs（7PJ′）碰撞转移截面

Cs蒸气置于十字交叉加热炉中,充入不同气压的H2,激光双光子激发Cs原子至6D3/2态,利用原子荧光光谱方法,研究了H2诱导6DJ→7PJ,的碰撞能量转移。测量不同氢气密度下直接6D3/2→6P3/2和敏化6D5/2→6P3/2,7P3/2→6S1/2和7P1/2→6S1/2的时间积分荧光强度,利用四粒子的速率方程分析,得到了6D3/2→7P3/2,6D3/2→7P1/2,6D5/2→7P3/2和6D5/2→7P1/2碰撞转移截面分别为(3.1±0.8)×10-16,(1.7±0.4)×10-16,(1.5±0.4)×10-16,(1.3±0.3)×10-16cm2。7PJ′态的猝灭截面分别为(2.5±0.6)×10-16cm2(对7P3/2)和(4.0±1.0)×10-16cm2(对7P1/2),它们主要是通过Cs(7PJ′)+H2→CsH+H反应产生的,而反应的相对活动性顺序为7P1/2>7P3/2。

激发态Cs(5D)原子间碰撞能量转移

用激光二步激发Cs原子至8S态,从谱线的波长及强度可以确定Cs原子的辐射及碰撞过程,5D态主要是由8S→7P→5D跃迁布居的.在1016-1017Cs密度范围内,测量了碰撞能量合并5D+5D→nL+6S(nL=9D,11S,7F)速率系数,因5D→6P(3.0-3.6μm)处于红外本实验不能探测,利用一个已经测量过的过程(即6P+5D→6S+7D)作相对测量,对于9D,11S和7F态,其平均速率系数分别为(8.4±4.2)×10-10,(7.3±3.6)×10-10和(9.7±4.8)×10-10cm3s-1.讨论了碰撞转移过程11S+6S 7F+6S对速率系数的影响.

激光辅助的快质子对氢原子的碰撞电离

在质心参考系中研究了激光场中 1MeV质子对基态氢原子的碰撞电离过程 .靶原子的缀饰波函数由含时间微扰论给出 ,末道出射电子态用双中心Coulomb Volkov波函数描述 .计算表明辐射场使出射电子的双重微分截面变小 .敲出电子的能量越高 ,截面减小越明显 。

寡肽的快原子轰击和碰撞活化质谱法分析

快原子轰击(FAB)软电离技术与碰撞活化(CA)技术联合用于寡肽中氨基酸顺序分析。在FAB质谱中出现明显的准分子离子峰(M+H)^+和(M+Na)^+,但碎片离子峰较微弱。然而在(M+H)^+离子的CA谱中有着明显的结构特征碎片离子峰,从而可明确地提供分子中氨基酸顺序的信息。这一技术可成为分析毫微摩尔寡肽氨基酸顺序的简便方法。曾以两个寡肽谷胱甘肽和五肽胃泌素作为例子研究了这一技术的应用。

快原子轰击和电喷雾电离质谱表征烷基苯磺酸盐

用负离子化快原子轰击（ＦＡＢ）和电喷雾电离（ＥＳＩ）质谱并结合碰撞活化解离（ＣＡＤ） 质谱方法对烷基苯磺酸盐（ＡＢＳ）进行鉴定。试样在负离子电喷雾电离（ＥＳＩ）过程中不产生碎 片峰，但是在ＦＡＢ过程中产生许多碎片，比较这些谱图，就可以区别碎片峰和分子离子峰。 线性或文化烷基苯磺酸盐的结构与相对含量可以在负离子ＥＳＩ／ＣＡＤ－ＭＳ方法中得到。负离 子ＥＳＩ－ＭＳ是快速、有效和可靠的鉴定ＡＢＳ的方法。

Rb蒸气中激光诱导5P和5D态的布居数变化

在Rb蒸气中观察了荧光强度的增强与减弱.5P3/2态荧光的减弱是由于激光激发5P3/2—→5D5/2的跃迁造成的,5D5/2态原子碰撞转移到5D3/2,产生5D3/2—→5P1/2的辐射,增加了5P1/2态的布居,从而使5P1/2—→5S1/2的荧光增强.激光诱导布居数的变化由相应荧光的强度信号的增减来检测,利用速率方程组,得到了受激发射(即5D5/2—→5P3/2)速率为2.0×108s-1,精细结构碰撞转移(即5D5/2—→5D3/2)截面为6.4×10-14cm2.

里德伯Cs原子与CCl_4分子的碰撞电离研究

为描述里德伯Ｃｓ原子与ＣＣｌ４分子碰撞电离实验研究中所发现的若干特征，对里德伯原子与分子碰撞的理论模型———准自由电子模型提出两点修正：（１）考虑原子实在碰撞过程中的作用，并且计入量子亏损；（２）考虑碰撞后正负离子的分离几率。利用修正的模型进行了理论计算，得到了与实验测量较为吻合的结果。

Ab initio calculation on accurate analytic potential energy functions and harmonic frequencies of c^3∑g^＋ and B^1-Пu states of dimer 7Li2

The comparison between single-point energy scanning （SPES） and geometry optimization （OPT） in determining the equilibrium geometries of c^3∑g^＋ and B^1-Пu states of dimer 7Li2 is made at numerous basis sets by using a symmetryadapted-cluster configuration-interaztion （SAC-CI） method in the Gaussian 03 program package. In this paper the difference of the equilibrium geometries obtained by SPES and by OPT is reported. The results obtained by SPES are found to be more reasonable than those obtained by OPT in full active space at the present SAC-CI level of theory. And the conclusion is attained that the cc-PVTZ is a most suitable basis set for these states. The calculated dissociation energies and equilibrium geometries are 0.8818 eV and 0.3090 nm for c^3∑g^＋ state, and 0.3668 eV and 0.2932 nm for B^1-Пu state respectively. The potential energy curves are calculated over a wide internuclear distance range from about 2.5α0 to 37α0 and have a least-squares fit into the Murrell-Sorbie function. According to the calculated analytic potential energy functions, the harmonic frequencies （We） and other spectroscopic data （ωeXe, Be and αe） are calculated. Comparison of the theoretical determinations at present work with the experiments and other theories clearly shows that the present work is the most complete effort and thus represents an improvement over previous theoretical results.

A modification potential method of calculating total cross sections of electrons scattering from complex molecules C2H6, C2F6, C6H6 and C6F6 at 100 eV-5000 eV

A complex optical model potential modified by incorporating the concept of bonded atom, which takes into consideration the overlapping effect of electron clouds between two atoms in a molecule, is first employed to calculate the total cross sections for electrons scattering from such complex molecules as C2H6, C2F6, C6H6 and C6F6 using the aclditivity rule model at Hartree-Fock level over the energy range from 100 eV to 5000 eV. The total cross sections are quantitatively compared with those obtained by experiments wherever available, and they are in good agreement with each other over a wide energy range. It is shown that the modified potential together with the additivity rule model is completely suitable for the calculation of total cross sections of electrons scattering from such complex molecules as C2H6, C2F6, C6H6 and C6F6 above 200 eV-300 eV.