The scattering of slow atoms by light

A kinetic equation has been obtained describing the motion of atoms in a resonant field of standing light wave. This equation is used to describe the scattering of atoms for conditions close to experimental ones [1]. It is shown that the dependence of atomic scattering has a dip at the resonance frequency of the field.     

Resonance line transfer and transport of excited atoms—II. Self-consistent solutions (1)

This second part of our study of non-LTE line transfer with convective transport of excited atoms presents self-consistent solutions of the radiative transfer equation and the kinetic equation of the excited two-level atoms, for the limiting case of no elastic velocity-changing collisions of the excited atoms. Pure Doppler broadening of the spectral line is assumed. We investigate reflecting and destroying boundaries for the excited atoms, while the boundary condition for the photons corresponds to free photon escape from the system. Our numerical procedure for solving the two coupled kinetic equations for the excited atoms and the photons is an iterative method using variable Eddington factors, and is described in detail. We present a simple model that considers the gas of excited atoms and the radiation field as two interacting fluids, which yields a straightforward interpretation of the various scale lengths encountered in the numerical results for the hydrodynamic properties (density, flux density, mean velocity) of the gas of excited atoms.     

Superradiance from three-level systems in atomic coherent state representation

A Fokker-Planck equation describing the coherent spontaneous emission from a system of 3-level atoms is derived using the atomic coherent states representation. The variables in this equation correspond directly to the number of atoms in the two excited states. The corresponding Langevin equations are discussed and their solutions for some special cases are presented.     

Analytically solving the relativistic Dirac-Coulomb equation for atoms and molecules

A method of solving the Schr?dinger equation in an analytically expanded form reported previously is extended to the relativistic case and a general method of exactly solving the Dirac-Coulomb equation has been proposed for atoms and molecules. Some problems characteristic of the relativistic case are discussed. Test applications to the hydrogen-like, helium-like atoms are satisfactory, implying a high potentiality of the proposed method also for the relativistic case.     

A novel fluid–wall heat transfer model for molecular dynamics simulations

The ‘fluid–wall thermal equilibrium model’, to numerically simulate heating/cooling of fluid atoms by wall atoms, is used to compare molecular dynamics simulation results to the analytical solution of 1-D heat equation. Liquid argon atoms are placed between two platinum walls and simultaneous heating and cooling is simulated at the walls. Temperature gradient in liquid argon is evaluated and the results are found to match well with the analytical solution showing the physical soundness of the proposed model. Additional simulations are done where liquid argon atoms are heated by both the walls for two different channel heights and it is shown that in such cases, heat transfer occurs at a faster rate than predicted by heat equation with decreasing channel heights.     

Resonance line transfer and transport of excited atoms—III. Self-consistent solutions (2)

In this last part of our study on non-LTE line transfer with convective transport of excited atoms, we present self-consistent solutions of the radiative transfer equation and the kinetic equation of the excited two-level atoms when the excited atoms undergo elastic velocity-changing collisions. We assume pure Doppler broadening of the spectral line and investigate reflecting and destroying boundaries for the excited atoms. Concerning elastic collisions of the excited atoms, our study covers all cases, from a collisionless gas (free particle streaming) discussed in Part II of this series of papers to a collision- dominated gas with the limiting case of complete redistribution. We present arguments that the streaming pattern of the gas of excited atoms does not depend critically on the shape of the line profile. Therefore, our results for a pure Doppler profile may also be used for other line profiles (Voigt, Lorentz) in first approximation, at least when the streaming parameter η is not too large.     

X-ray photoelectron spectroscopy of merocyanine dyes: Part IV. Correlation of O1s binding energy with atomic charge calculated by Smyth's method. Application to the merocyanine 540 dye

Smyth's equation for calculating the partial ionic character of bonds yields better results than Pauling's equation when the electronegativity difference between the bonded atoms exceeds unity. This equation is used to establish the following binding energy/partial charge correlation for the O1s line:O1s binding energy (eV) = 534.55 + 3.29 q. This relation is used to evaluate the conjugation of benzoxazolinic and carbonyl oxygen atoms in the MC 540 dye from the measured XPS binding energies. The partial charge on the carbonyl oxygen atoms is close to −1 and the weight of the ⁻O-C⩽ form can be evaluated to ca. 80%.     

Superradiance and energy transfer within a system of atoms

We investigate cooperative effects in energy relaxation and energy transfer for N atoms in a thermal radiation field with superradiance master equations as well as a closed set of coupled moment equations. Both spatially large and spatially small systems are considered. For small systems nonlinear rate equations for the energy are related to the moment equations. Symmetry of the small system to interchanging atoms is used to incorporate off-diagonal solutions of the superradiance master equation in expressions for the probability of the transfer of energy from one group of atoms to another. The long time excitation probability for initially unexcited atoms is large and strongly correlated. Cooperative processes in a large system which fall off with the distance between a cooperating pair of atoms include energy loss and transfer terms in the master equation. The energy transfer is oscillatory in time. Energy relaxation is shown by numerical solution to become cooperative in a very sudden manner as the scale of the atomic system is decreased through the resonant wavelength.     

Quantum Dynamics of Cooled Atoms in the Presence of Bose—Einstein Condensates

Under the Markov approximation,the quantum dynamics of cooled atoms in the presence of Bose-Einstein condensates is studied.A master equation governing the evolution of such a system is derved.Using this master equation,the distribution of the atoms in the excited states at finite temperature and the dynamics of the excited atom at zero temperature are given and discussed.     

Polarization and trapping of weakly bound atoms in penning trap fields

The ATHENA and ATRAP groups at CERN recently reported the production of weakly bound antihydrogen atoms in a non-neutral positron-antiproton plasma. This Letter derives an equation of motion for weakly bound atoms in the electric and magnetic fields of the plasma and trap. The atoms are polarized by the electric field and can be trapped radially in the edge region of the plasma where the electric field is maximum.     

Self-sputtering of thin films (Application of the invariant immersion method)

The analytic solution to the problem of self-sputtering of thin homogeneous films is considered. Invariant immersion principles were used for deriving integral equations describing the flow of sputtered atoms. Approximate solutions of the integral equation are found for the functions describing the spectra of atoms emitted from the film surface in the case of self-sputtering.     

The effect of spatial dispersion and boundaries of a medium on resonance radiation transfer

An integral equation is derived for the spectral density of excited atoms using optically dense bounded dispersion media as an example. It is found that the inclusion of the thermal motion of atoms and of the effects due to the existence of a boundary brings about a nonlocal correlation between the concentration of excited particles and the intensity of electromagnetic field in the medium. It is demonstrated that, when the spatial dispersion of permittivity and the boundary effects are disregarded, the obtained result transforms to the well-known Biberman-Holstein equation. The problem on the spectral intensity of radiation of a heated half-space is also investigated.     

Dynamics of the collective spontaneous emission of two three-level atoms in a cavity

Based on the master equation for the density matrix, the collective spontaneous emission of two A-type three-level atoms interacting with two modes of a quantum electromagnetic field in a finite-Q cavity is studied. The evolution of the emission intensity for each mode is found for the case where both atoms are initially in the excited state.     

符号关系式在测定含重原子晶体结构中的应用——Ⅰ.一个符号修正方案

对于由序数相近的原子所构成的晶体,Sayre等式给出了衍射结构振幅之间的关系。在测定由碳、氮、氧等“轻”原子构成的中心对称晶体结构中,利用Sayrs等式曾获得不少结果。但是对于含“重原子’的晶体,Sayre等式即不再适用。此时通常都利用所谓“重原子法”来解结构。本文讨论了含重原子情况下,晶体的结构振幅符号、Sayre符号,以及重原子符号之间的关系,从而指出了将重原子法和Sayre法结合的可能性,并提出了一个结构振幅符号的循环修正方案,借此有可能从重原子符号或一套包含若干错误的结构振幅符号出发,不经过电子密度综合而最终获得正确的结构振幅符合。将此方法试用于一个假想的一维晶体结构,效果良好。本文还讨论了有关在实际的晶体结构测定中应用的若干问题。