On the binding of atoms with antiatoms

The stability of X⁺Y⁺X^?Y^? Coulomb molecules consisting of X⁺Y^? atoms and X^?Y⁺ antiatoms to dissociation is studied. On the basis of multiparameter variational calculations, it is found that such molecules are stable to dissociation into X⁺X^? atoms and Y⁺Y^? antiatoms if the mass ratio of particles X and Y lies in the range 0.4710<m _X /m _Y <2.1231. The e⁺e⁺e^?e^?, π⁺μ⁺π^?μ^?, t⁺d⁺t^?d^?, p⁺K⁺p^?K^?, and d⁺p⁺d^?p^? molecules satisfy this condition.     

Double jumps and transition rates for two dipole-interacting atoms

Cooperative effects in the fluorescence of two dipole-interacting atoms, with macroscopic quantum jumps (light and dark periods), are investigated. The transition rates between different intensity periods are calculated in closed form and are used to determine the rates of double jumps between periods of double intensity and dark periods, the mean duration of the three intensity periods and the mean rate of their occurrence. We predict, to our knowledge for the first time, cooperative effects for double jumps, for atomic distances from one and to ten wave lengths of the strong transition. The double jump rate, as a function of the atomic distance, can show oscillations of up to 30% at distances of about a wave length, and oscillations are still noticeable at a distance of ten wave lengths. The cooperative effects of the quantities and their characteristic behavior turn out to be strongly dependent on the laser detuning. Received 19 March 2001 and Received in final form 13 June 2001     

Pair excitation of atoms in radiative collisions

The kind of radiative collision in which two atoms are simultaneously excited by one photon is considered. The experiment on observation of this effect is proposed.     

Absolute ionization rates of multielectron transition metal atoms in strong infrared laser fields

We report on nonresonant strong field ionization of the multielectron transition metal atoms V, Nb, Ta, Ni, and Pd. Operating in the adiabatic regime (lambda = 1.5 microm), we quantitatively determined both (i) the first charge state saturation intensities and (ii) the absolute ionization rates for intensities ranging from threshold up to 3 x 10(14) W/cm2. We observed a dramatic suppression of ionization relative to single active electron approximation expectations. We suggest that this derives from dynamic polarization or screening effects within the multielectron atom, stressing a need for many-body theories of strong field ionization.     

Calculation of collisional and radiative transition probabilities between excited argon levels

Average radiative transition probabilities for argon atoms have been calculated for transitions between 24 levels in two groups characterized by the atomic core terms ²P_1/2 and ²P_3/2 by using the method of Bates and Damgaard. The results are compared with data in the NBS tables (Wiese et al.) and with those of Katsonis and Drawin. We find satisfactory agreement for the order of magnitude, even for transitions between lower lying levels. Parameters, which appear in Drawin's semiempirical cross-section expressions for electronic excitation of optically allowed and parity-forbidden transitions, are determined with the multipole expansion method proposed by Sobel'man for transitions between the specified levels. Most of these are easily obtained, but the method must be improved for transitions between levels having the same azimuthal quantum number because the summation over the constituent terms does not converge.     

稀土原子与离子的自然辐射寿命测量

概述了当前自由原子和离子的激发态自然辐射寿命测量技术的进展。以LaⅠ和PrⅡ为例,系统介绍了几种稀土元素自由原子和离子激发态寿命测量技术并分析了它们的优缺点;以SmⅡ为例,详细介绍了激光烧蚀产生自由原子(离子)技术及结合激光诱导荧光时间分辨光谱技术进行激发态寿命测量的优缺点。最后,探讨了改进上述技术局限性的解决思路,以期进一步提高辐射寿命测量的精确度。     

Field-theoretical treatment of approximations to radiative transitions in atoms

Starting with a field-theoretical many-body definition of eigenvalues and radiative transition matrix elements for atomic systems, a systematic approach is taken to approximations of the exact results. The guiding principle is the maintenance of gauge invariance (GI) in radiative transition S matrix elements. At the level of the one Coulomb exchange approximation in both the one-electron and the electron-hole propagator kernels, one obtains the well-known Hartree-Fock (HF) and random phase approximations (RPA). A detailed discussion and comparison of various approaches to RPA is made, in the case of both N and N ? 1 electron shielding (the regular HF and HF with frozen relaxed core—FRC). In the former case, a new and considerably simpler form of the RPA equations are obtained than heretofore proposed equivalent forms. Finally, a different approximation than the usual HF and RPA, involving higher-order correlations, is developed to illustrate how such approximations can be systematically generated.     

On the interaction between chemisorbed atoms at transition metal surfaces

A model hamiltonian is derived describing the interaction of two adsorbates. The nonorthogonality of the basis set is converted into a renormalization of the matrix elements. The interaction energy, direct and indirect of two hydrogen atoms and single particle spectral densities are calculated for adsorption on a semi infinite simple cubic solid. Correlation effects are included by a variational ansatz.     

All-order transition amplitudes in many-electron atoms

All-order expressions for transition amplitudes are obtained from the exact re-summation of three-operator perturbation series. They are formulated in terms of continued fractions where the role played by the non-central part of the many-electron atom potential is shown explicitly.     

XeI and XeII radiative lifetimes and transition probabilities

The lifetimes of ten levels of the xenon atom and two levels of the ion were measured. The probabilities for several transitions are calculated. The effective decay cross section is calculated for collisions for the 2p₈ level of the xenon atom.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 3, pp.24–29, March, 1971.The authors thank V. S. Mel'chenko for assistance in this study.     

Relativistic radiative transition rates and energies for the Li-like isoelectronic sequence: Electric and magnetic dipole and quadropole radiation

For Li-like ions in the isoelectronic sequence between the nuclear charges Z = 26 and 94, energies, oscillator strengths and probabilities of electric and magnetic dipole and quadropole transitions between the first 22 atomic levels were calculated by means of the multiconfigurational Dirac-Fock model. The effects of nonlocal Breit interaction, electron self-energy and vacuum polarization were included in calculating energy levels and radiative rates. The trends of transition energies and rates along the isoelectronic sequence, in particular, the enhancement of the forbidden transitions with increasing atomic number Z, are discussed.     

Atomic radiative transition probabilities in a continuous medium

A simple quantization procedure is applied to the electromagnetic radiation field in a nondissipative, weakly dispersive continuous medium. The resulting operator expressions for the electric and magnetic field strengths are used to study the influence of the dielectric and magnetic properties of the medium on the Einstein coefficients for spontaneous and stimulated radiative transitions of single atoms or molecules embedded in the medium. The expressions obtained are consistent with detailed-balance considerations.     

Effective charges for radiative and Auger transition probabilities

Analyses of higher-order resonant, atomic collision processes require many accurate radiative and Auger transition probabilities, A_r and A_a. Numerical evaluation of these probabilities for high Rydberg states and for large angular momenta is difficult. We develop here Coulombic expressions for A_r and A_a, with effective charges for the individual orbitals involved. Simple formulas for the effective charge are proposed and tested against the more accurate data obtained with Hartree—Fock wave functions.     

Formation of fast exotic atoms by radiative Coulomb capture

Interesting surprises in some exotic atom kinetics have been reported recently. These involve muonic atom transfer cross sections, nuclear pion capture and theq 1s effect in CF. These can be explained if the exotic atom population contains a contributing fast component. Such fast atoms can be formed by radiative continuum to bound transitions of fast (keV) muons or pions. Cross sections for formation of such fast pionic and muonic atoms and their velocity distributions are reported. The possibility of these processes competing with the thermalisation channels and contributing effectively to the exotic atom population is discussed.     

Inhomogeneous depth distribution of fluorine atoms in PVDF upon radiative carbonization

Under the action of ionizing radiation on a PVDF film, fluorine and hydrogen atoms bound to its linear carbon chain with single chemical bonds detach. Free atoms and HF molecules diffuse toward the film surface and escape from it. As a result of irradiation of the sample surface, a fluorine concentration depth profile arises. The fluorine distribution in the PVDF films subjected to long-term X-ray exposure was studied using X-ray photoelectron spectroscopy and Rutherford backscattering spectroscopy. Both methods yield close values of the fluorine concentration at a depth of ～10 nm.     

Auger and radiative transition probabilities of high Rydberg states

The dependence of the Auger and radiative transition probabilities of high Hydberg states on their principal and orbital quantum numbers n and l is studied. Based on explicit calculations, a simple empirical l-dependence of the gaussian type is obtained, which differs drastically from any of the previously assumed behavior.