Radiative Recombination Rate Coefficients Research Articles

A Review of Radiative and Dielectronic Recombination for C and O Ions

Theoretical calculations of radiative and dielectronic recombination rate coefficients for carbon and oxygen ions are reviewed. For radiative recombination into excited states, various hydrogenic formulae for recombination are considered, and results for total rates obtained by using explicit calculations of photoionization cross sections from the ground states of these ions in conjunction with such hydrogenic formulae are reported. For dielectronic recombination, the isolated-resonance approximation for the calculation of cross sections and rates is discussed, and rate coefficients for several carbon and oxygen ions are presented. The effects of electric fields and electron density on dielectronic recombination rates are considered.

Inhibited and enhanced spontaneous emission from optically thin AlGaAs/GaAs double heterostructures.

Inhibited spontaneous emission in atomic physics has been intensively investigated recently. In solid-state physics these effects are no less important. We have studied the spontaneous emission of light from electron-hole recombination in optically thin GaAs double heterostructures. The electron-hole radiative recombination rate coefficient $B$ is not purely a property of the GaAs itself, but depends strongly on the optical-mode density and refractive index of the medium in which it is immersed. The spontaneous-emission rate can be markedly increased or decreased depending on whether the surrounding refractive index is higher or lower than that of GaAs.

The influence of core fine-structure interactions on dielectronic recombination at low temperatures: B-like C, N and O recombined ions

The author uses the program AUTOSTRUCTURE to calculate configuration-mixing intermediate-coupling effective dielectronic recombination rate coefficients for the recombined ions C+ N2+ and O3+ at temperatures T=103-6.3*104 K. The author tabulates results for the quartet-quartet transition lines-these do not arise in LS coupling at low densities applicable to gaseous nebulae-as well as selected doublet-doublet lines. The author also compares total rate coefficients for both direct radiative recombination and dielectronic recombination, the latter being calculated in both LS and intermediate coupling.

Radiative recombination in rubidium

The rate coefficients for radiative recombination of Rb into individual ground and excited nl states (n<or=20, l<or=10), summed over l<n(n<or=10) and over all states, have been computed for the electron temperature range 500<or=T<or=6000K. Using the principle of detailed balance, photoionisation cross sections of Rb calculated in the framework of a single-electron model have been used. The evolution with n and l for given T, with T for given n and various l and with T of the total radiative recombination is analysed. The significant non-hydrogenic features for recombination are outlined. Comparisons are made with the results of the hydrogenic and kramers' models and with other results available for alkali atoms.

Direct radiative recombination of electrons with atomic ions: Cross sections and rate coefficients

Simple expressions are obtained which permit systematic estimates of the rate coefficients for direct radiative recombination (DRR) of fast electrons with atomic ions of various ionic species. The analysis utilizes a set of cross sections obtained through numerical calculations combined with the use of an interpolation scheme to smoothly connect reduced cross sections (apart from normalizations) of the bremsstrahlung tip region and the low-lying DRR region. It is shown that these numerical cross sections can be reproduced by the predictions of a modified semiclassical Kramers formula with an appropriate effective charge ${Z}_{\mathrm{eff}}$, which is larger than the effective charge which reproduces the energy levels of the states into which capture occurs. In accord with this modified Kramers formula, the numerically obtained total cross sections are shown to scale with $\frac{{Z}_{\mathrm{eff}}^{2}}{K}$ for each isoelectronic sequence, and with a parameter ${({n}_{0})}_{\mathrm{eff}}$ which characterizes each isoelectronic sequence. Using these scaling properties, simple analytic expressions are obtained for recombination rate coefficients, for the rate of electron kinetic-energy loss, and for the rate of radiated power loss, assuming a classical Maxwell-Boltzmann thermal distribution of continuum electrons.

Collisional radiative recombination in high-pressure noble gas mixtures

Rate coefficients are calculated for neutral-assisted collisional radiative recombination in dense, weakly ionized rare-gas mixtures using the quasiequilibrium model developed by Bates. It is shown that the recombination rate can be significantly altered by the presence of a buffer gas. In particular, the presence of helium can enhance the collisional radiative recombination rate coefficient of heavy rare gases by a factor of 5.

On Dielectronic Recombination in Some Coronal Ions

Abstract Dielectronic recombination rate coefficients for some ions found in the solar corona have been investigated in the temperature range 20-1000 eV using two different expressions. A comparison has also been made with the corresponding radiative recombination rate coefficients.

Dielectronic recombination in sodium iso-electronic sequence

Dielectronic recombination rate coefficients for some members of the sodium iso-electronic sequence have been investigated in the temperature range 2–1000 eV using two different expressions. A comparison has also been made with the corresponding radiative recombination rate coefficients.

Partial Photoionization Cross Sections and Radiative Recombination Rate Coefficients for Lithium-Like Ions

Partial photoionization cross sections and radiative recombination rate coefficients corresponding to n = 2, 3, 4, and 6, and 1 &lt; n, have been obtained on the basis of the nonhydrogenic single-electron model for lithium-like ions with Z = 6, 8, 13, 26, and 42. Polynomials for interpolating the partial cross sections to intermediate values of Z are given. Comparisons made with nonrelativistic dipole hydrogenic model results indicate that that model is of limited usefulness. Deviations of more than 10% from classical Kramers model rate coefficients were found for Li-like C(kT&gt; 0.03 keV), O(kT&gt; 0.1), and Al(kT&gt; 1.0). Subject headings: atomic processes - transition probabilities

Calculated spectral dependence of gain in excited GaAs

The calculated dependence of the gain coefficient on photon energy and excitation level in GaAs is given for 297 and 77 K. The curves of gain versus excitation rate generally have downward curvature for photon energies near the gain peak, while the envelope of these curves generally has upward curvature except at high excitation rates. Results are also given for the calculated dependence of the radiative recombination rate coefficient and of the photon energy at the gain peak on excitation rate. The qualitative behavior of the results is in agreement with experiment.

Recombination between electrons and atomic ions, I. Optically thin plasmas

Consideration is given to the interacting collisional and radiative processes occurring in a plasma. A statistical theory describing the general loss mechanism, for which the name collisional-radiative recombination is proposed, is described. This theory enables the collisional-radiative recombination coefficient a to be determined knowing the relevant spontaneous transition probabilities and the rate coefficients for radiative recombination and collisional excitation and ionization. Detailed calculations are carried out on hydrogen-ion plasm as which are optically thin. It is found that α is an increasing function of the number density of free electron n(c) the increase being especially marked if the electron temperature T is low; for example, if T is 250 °K α becomes almost 20 times as great as the radiative recombination coefficient (which describes the loss in a very tenuous plasma) when n(c) is only about 10 8 /cm 3 , whereas if T is 64 000°K a does not become as great as this until n(c) is about 10 18 /cm 3 . From a similar investigation in which the ground level of the hydrogen atom is made inaccessible (in crude representation of an alkali atom) it is inferred that the value of a is probably not very sensitive to the species of singly charged ion involved. Recombination of electrons with bare nuclei of charge Ze to form hydrogenic ions is similarly treated for an optically thin plasma. It is shown that to a close approximation the reduced coefficient α/ Z is a function of a reduced tem perature T/Z 2 and a reduced number density n(c)/Z 7 only. The values of the reduced coefficients are of com parable m agnitude and have a similar dependence of the reduced temperature and density as the coefficients for hydrogen ion plasmas. The variation of the recombination coefficient α with Z in the same plasma (i.e. same n(c) and T ) is investigated. It may be expressed in the form a α ∝ Z z where the index z depends on n(c) and T . Though z is generally positive as would be expected, it is negative if n(c) and T are very high. A physical explanation of this is presented.