Electron-ion Recombination Rate Coefficients Research Articles

Electron‐Ion Recombination of Neutral Iron

The total and state-specific electron-ion recombination rate coefficients are obtained for Fe I. The calculations are carried out using a new ab initio method that incorporates both the radiative and the dielectronic recombination processes in an unified and self-consistent manner. The computations employ the close coupling approximation and the R-matrix method from atomic collision theory. A 52 state close coupling eigenfunction expansion dominated by the states of the ground 3d64s and excited 3d7, 3d64p, 3d54s2, and 3d54s4p configurations of Fe II are used in the present calculations. The important electron correlation and radiation damping effects are included via explicit coupling of autoionization and radiative channels. This is the first detailed atomic calculation for the recombination rates for Fe I. The present rates are considerably higher than the radiative recombination rates being used currently in the low-temperature region, T ≤ 104 K, whereas they are about 4 times lower than those given by the Burgess general formula for dielectronic recombination at higher temperatures. The implications of the new recombination rate coefficients and photoionization cross sections for Fe I on the ionization structure of iron in the cold neutral interstellar medium are studied. It is found that the ratio of Fe II to Fe I obtained with the new atomic data increases by a factor of about 3-30 over previous calculations.

Electron‐Ion Recombination of Fe v

Ionization balance in the low-ionization stages of iron is important in a variety of astrophysical plasmas. Accurate recombination rates are needed but are difficult to compute in a detailed quantum mechanical treatment. The main difficulty lies in the complexity of strong electron-electron correlation arising due to the open 3d shell. We present the total electron-ion recombination rate coefficients for the process, e+Fe VI → Fe V, obtained in an ab initio manner. Large-scale computations are carried out in the close coupling (CC) approximation using the R-matrix method employing a unified treatment that considers the infinite number of states of the recombined ion and incorporates both the radiative recombiantion (RR) and the dielectronic recombination (DR) processes in a self-consistent manner. It involves calculations of detailed photoionization cross sections, σPI, with autoionizing resonances of a large number of bound states with n≤nmax, such as 1054 bound states for the present case of Fe V. The number also equals the total number of state-specific recombination rates obtained for the ion. The high-n states are treated through the DR theory by Bell & Seaton. The same wavefunction expansion is employed in all photoionization/recombination calculations, thereby ensuring self-consistency. Rates are presented at a wide range of temperature for all practical applications. Present rates for total recombination differ considerably from currently used values obtained using simpler approximations. Application of the new recombination rate coefficients and photoionization cross sections for the ionization structure of iron in planetary nebulae show that under typical conditions the relative fractions of Fe V and Fe VI change by nearly a factor of 2.

Photoionization cross sections and oscillator strengths for Fe

Ab initio calculations are carried out for the photoionization cross sections and oscillator strengths for Fe III in the close-coupling approximation employing the R-matrix method. A 49-state eigenfunction expansion for Fe IV, with states dominated by the ground configuration 3${\mathit{d}}^{5}$ and the excited configurations 3d${\mathrm{}}^{4}$4s and 3d${\mathrm{}}^{4}$4p, is employed to ensure an extensive treatment of autoionizing resonances and other electron correlation effects related to channel couplings that considerably affect the effective cross sections. Of particular interest are the wide resonances due to photoexcitation within the core states that enhance the background cross sections by orders of magnitude at high energies. Coupled wave functions are obtained for 805 bound states of Fe III below the first ionization threshold; all of the 199 LS terms observed experimentally have been identified. Photoionization cross sections, with detailed autoionizing resonances, are obtained for the computed bound states as a function of photoelectron energy. The present results also include the oscillator strengths for 11 979 transitions between the bound states of Fe III that lie below the ionization threshold. In addition, the partial photoionization cross sections for 239 bound states, with the residual ion in the ground state, are also obtained. These cross sections are computed for applications to the determination of electron-ion recombination rate coefficients and population of levels in collisional-radiative models that do not assume local thermodynamic equilibrium. The present radiative data are compared with the observed energy values, lifetimes, and the photoionization cross sections calculated by others. \textcopyright{} 1996 The American Physical Society.

Electron-Ion Recombination Rate Coefficients for SI i, SI ii, S ii, S iii, C ii, and C-like Ions C i, N ii, O iii, F iv, NE v, NA vi, MG vii, AL viii, SI ix, and S XI

view Abstract Citations (72) References (16) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Electron-Ion Recombination Rate Coefficients for Si I, Si II, S II, S III, C II, and C-like Ions C i, N II, O III, F IV, Ne V, Na VI, Mg VII, Al VIII, Si IX, and S XI Nahar, Sultana N. Abstract A new unified treatment for electron-ion recombination is employed to obtain recombination rate coefficients for silicon, sulfur, and carbon ions of importance in the study of the interstellar medium and H II regions in general. Improved and extended results are also presented for ions in the carbon isoelectronic sequence. Recombination rate coefficients are tabulated at a wide range of temperatures, from 101 to l09 K. These rates correspond to total electron-ion recombination incorporating both the radiative and dielectronic recombination processes calculated in an ab initio manner. Publication: The Astrophysical Journal Supplement Series Pub Date: December 1995 DOI: 10.1086/192248 Bibcode: 1995ApJS..101..423N Keywords: ATOMIC DATA; ATOMIC PROCESSES full text sources ADS | Related Materials (1) Erratum: 1996ApJS..106..213N

New results for photoionization and recombination of astrophysically abundant atoms and ions - The carbon sequence

view Abstract Citations (11) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS New Results for Photoionization and Recombination of Astrophysically Abundant Atoms and Ions: The Carbon Sequence Nahar, Sultana N. ; Pradhan, Anil K. Abstract Photoionization cross sections and electron-ion recombination rate coefficients are presented for carbon-like ions obtained using methods developed for the Opacity Project. Extensive autoionization resonance structures and partial photoionization into specific states of the residual ion. It is shown that the excited state photoionization cross sections are not, in general, described by hydrogenic behavior and often contain strong resonances due to photoexcitation corresponding to dipole transitions in the core ion. A new method is described for calculating total recombination rate coefficients that accounts for both the radiative and the dielectronic recombination processes in an ab initio manner. Recombination rate coefficients are presented for C I, N II, O III, F IV, and Ne V at a wide range of temperatures for astrophysical applications. Publication: The Astrophysical Journal Pub Date: October 1992 DOI: 10.1086/171828 Bibcode: 1992ApJ...397..729N Keywords: Abundance; Carbon; Interstellar Chemistry; Photoionization; Recombination Reactions; Autoionization; Ground State; Ionization Cross Sections; Molecular Excitation; Photoexcitation; Quasars; Stellar Atmospheres; Atomic and Molecular Physics; ATOMIC DATA; ATOMIC PROCESSES full text sources ADS |

Electron-ion recombination in the close-coupling approximation.

A computational formalism is presented to obtain total electron-ion recombination cross sections and rate coefficients employing the close-coupling approximation for photoionization and scattering and the Bell and Seaton theory of dielectronic recombination. The results differ significantly from separate treatments of the two processes, radiative and dielectronic recombination. The R-matrix method, as developed for the Opacity Project, is used and results are presented for recombination collision strengths and rate coefficients for boronlike ${\mathrm{O}}^{2+}$ and ${\mathrm{Ne}}^{4+}$

Determination of the electron-ion dissociative recombination coefficients for several molecular ions at 300 K

The electron-ion dissociative recombination rate coefficients, alpha e, have been determined for ten molecular ions, seven of which have not previously been measured. The data were obtained under truly thermal conditions at 300 K using a flowing afterglow/Langmuir probe (FALP) apparatus. Recombination coefficients were obtained for the following ions: CO2+ ( alpha e=3.1*10-7 cm3 s-1), N2+ (2.0), CO+ (1.6), KrH+ (<0.2), XeH+ (<0.4), HSO2+ (2.7), CH3CNH+ (3.3), CH3CHOH+ (3.9), C2H5CNH+ (4.7) and ((CH3)2CO)2H+ (14). The dissociative recombination of many of the ions studied may be important in planetary, cometary and terrestrial atmospheres and be involved in the synthesis of interstellar molecules.

Ion aging effects on the dissociative-attachment instability in CO2 lasers

Onset of the dissociative-attachment instability requires that the rate coefficient for electron detachment (kd) from negative ions be below a critical value. The predominant negative and positive ions in a CO2∶N2∶He gas-discharge plasma are known to change with time. As secondary by-products form and the predominant negative-ion species changes from CO3− to NO2−, a decrease inkd occurs destabilizing the discharge. Since NO2− and NO3− are largely unreactive with respect to associative detachment,kd depends in a sensitive fashion on the concentration of certain minority negative ions (O−, O2−) and neutrals (CO, O, N). The sufficient conditions for the dissociative-attachment instability are much less sensitive to changes in the electron-ion and ion-ion recombination rate coefficients resulting from the ion aging process.