Recombination Rate Coefficients Research Articles

High photogeneration and low recombination rate leading to high-performance non-fullerene organic solar cells

TPV/TPC, EQE/IQE measurements and simulation modeling reveal that the high-performance organic solar cells originate from both an increasing charge generation and a reducing recombination rate coefficient, with PCE potentially exceeding 21%.

Dielectronic recombination data for dynamic finite-density plasmas

Dielectronic (DR) and radiative (RR) recombination rate coefficients for 19 phosphorous-like ions, between S+ and W59+, forming sulphur-like ions, have been calculated as part of the assembly of a level-resolved database necessary for modelling dynamic finite-density plasmas, within the generalized collisional-radiative framework. Calculations have been performed within the multi-configuration Breit-Pauli approximation using the code AUTOSTRUCTURE, from both ground and metastable initial states, in both LS coupling and intermediate coupling (IC), allowing for ∆n = 0 and ∆n = 1 core-excitations from the ground and metastable levels involved in the DR processes. Partial and total DR coefficients have been calculated for S+ to Zn15+, as well as Kr21+, Mo27+, Xe39+, and W59+. Results for a selection of ions from the sequence are discussed in this paper, and are compared with the existing theoretical and experimental results. Dielectronic recombination results for the Fe11+ resonance spectrum associated with ∆n = 0 core excitations are compared with those from merged-beam measurements. Fits to the total (IC) DR and RR rate coefficients are presented in tabular form. Partial LS and IC DR and RR rate coefficients are archived in the open access database OPEN-ADAS in standard ADAS adf09 and adf48 file formats, respectively.

Control of Dy164 Bose-Einstein condensate phases and dynamics with dipolar anisotropy

We investigate the quench dynamics of quasi-one and two dimensional dipolar Bose-Einstein condensates (dBEC) of $^{164}$Dy atoms under the influence of a fast rotating magnetic field. The magnetic field thus controls both the magnitude and sign of the dipolar potential. We account for quantum fluctuations, critical to formation of exotic quantum droplet and supersolid phases in the extended Gross-Pitaevskii formalism, which includes the so-called Lee-Huang-Yang (LHY) correction. An analytical variational ansatz allows us to obtain the phase diagrams of the superfluid and droplet phases. The crossover from the superfluid to the supersolid phase and to single and droplet arrays is probed with particle number and dipolar interaction. The dipolar strength is tuned by rotating the magnetic field with subsequent effects on phase boundaries. Following interaction quenches across the aforementioned phases, we monitor the dynamical formation of supersolid clusters or droplet lattices. We include losses due to three-body recombination over the crossover regime, where the three-body recombination rate coefficient scales with the fourth power of the scattering length ($a_s$) or the dipole length ($a_{dd}$). For fixed values of the dimensionless parameter, $\epsilon_{dd} = a_{dd}/a_s$, tuning the dipolar anisotropy leads to an enhancement of the droplet lifetimes.

Experimental Determination of the Dissociative Recombination Rate Coefficient for Rotationally Cold CH+ and Its Implications for Diffuse Cloud Chemistry

Observations of CH+ are used to trace the physical properties of diffuse clouds, but this requires an accurate understanding of the underlying CH+ chemistry. Until this work, the most uncertain reaction in that chemistry was dissociative recombination (DR) of CH+. Using an electron–ion merged-beams experiment at the Cryogenic Storage Ring, we have determined the DR rate coefficient of the CH+ electronic, vibrational, and rotational ground state applicable for different diffuse cloud conditions. Our results reduce the previously unrecognized order-of-magnitude uncertainty in the CH+ DR rate coefficient to ∼20% and are applicable at all temperatures relevant to diffuse clouds, ranging from quiescent gas to gas locally heated by processes such as shocks and turbulence. Based on a simple chemical network, we find that DR can be an important destruction mechanism at temperatures relevant to quiescent gas. As the temperature increases locally, DR can continue to be important up to temperatures of ∼600 K, if there is also a corresponding increase in the electron fraction of the gas. Our new CH+ DR rate-coefficient data will increase the reliability of future studies of diffuse cloud physical properties via CH+ abundance observations.

Total and state-specific electron-ion recombination rates and photoionization of Ca XV for high temperature plasma

The inverse processes of photoionization and electron-ion recombination of (Ca XV + hν↔ Ca XVI + e), are studied using the unified method of Nahar and Pradhan for a large number of bound states, 582 in total with n≤10 and l≤9, for their characteristic features particularly in the high energy region that can impact plasmas at high temperature. The unified method which implements close-coupling (CC) approximation and the R-matrix method includes both the radiative recombination (RR) and dielectronic recombination (DR) for the total recombination and yields self-consistent sets of results for both the inverse processes. The present study, carried out in large scale computations, employs a large CC wavefunction expansion of 29 LS states belonging to n=2,3 complexes of the core ion Ca XVI, and appeared to be the first detailed study for the electron-ion recombination of the ion. The present results include (i) state-specific photoionization cross sections (σPI(nLS)) leaving the core ion in the ground state, (ii) state-specific recombination rate coefficients (αRC(nLS,T)) that include both the RR and DR, (iii) total recombination rate coefficients (αRC) with temperature that include contributions of infinite number of recombined states, and (iv) a spectrum of total electron-ion recombination cross sections and rates with respect to photoelectron energy. The study finds that the core ion excitations from the ground to high n=3 states have introduced Rydberg resonances which are stronger and Seaton resonances which are more enhanced in the high energy region of σPI compared to those introduced by excitations to the n=2 states. Such features have contributed to the shape of the temperature dependent state-specific αRC(nLS,T), and have resulted in three DR bumps/ shoulders in the high temperature region of the total αRC(T) where the third DR bump at temperature of ∼ 4 MK has raised αRC(T) at high T above all previous rates. The results are expected to be accurate within 10%–15% and provide more complete and precise spectral modelings for the high temperature plasmas where the highly charged Ca XV is more abundant.

Low-Field Feshbach Resonances and Three-Body Losses in a Fermionic Quantum Gas of 161Dy

We report on the high-resolution Feshbach spectroscopy on a degenerate, spin-polarized Fermi gas of 161Dy atoms, measuring three-body recombination losses at a low magnetic field. For field strengths up to 1 G, we identify as much as 44 resonance features and observe the plateaus of very low losses. For four selected typical resonances, we study the dependence of the threebody recombination rate coefficient on the magnetic resonance detuning and on the temperature. We observe a strong suppression of losses with decreasing temperature already for small detunings from the resonance. The characterization of complex behavior of the three-body losses of fermionic 161Dy is important for future applications of this peculiar species in research on atomic quantum gases.

Silicon nanocluster anion-argon cation recombination via hybrid continuum-molecular dynamics calculations

Prediction of the charge distribution on particles in an aerosol is critical not only in electrical mobility based characterization methods, but also in understanding the role that charging plays in particle growth in gas phase synthesis reactors. The latter is particularly important in non-thermal plasma synthesis reactors, wherein nanoclusters form and grow from vapor phase precursors in a high electron and high ion density environment. In plasmas, because free electrons are much less massive and much more mobile than positive gas ions, nanocluster charge distributions are biased negative. However, neutral or even positively charged nanoclusters may exist, depending on the rate of nanocluster-gas ion recombination, and nanocluster-nanocluster collisions may greatly contribute to nanocluster growth if not Coulombically suppressed. To better understand the charge distribution on nanoclusters in non-thermal plasma synthesis systems, we applied a recently developed collision rate calculation method, i.e. the continuum-molecular dynamics (C-MD) method, to examine recombination of Sinz nanoclusters (n=47,91,266,&494, z=−1,&−2) and Ar+ cations at 300 K and pressures from 103.5−106 Pa, in argon neutral gas. With collision rate coefficients from the C-MD approach, nanocluster steady-state charge distributions were calculated. C-MD determined recombination rate coefficients are found to be higher than those from the traditionally-used limiting sphere theory approach of Fuchs outside of the continuum limit, leading to charge distributions which, although biased towards negative charge levels, are less biased than predicted by the traditional limiting sphere method, with differences particularly noticeable at lower pressures. Application of C-MD recombination coefficients in steady-state charge distribution calculations shows that the fraction of positively charged nanoclusters in a non-thermal plasma would be negligibly small; however, there is an appreciable fraction of neutral nanoclusters, and hence nanocluster-nanocluster collisions cannot be neglected in modeling particle growth in plasma reactors.

Effect of fluorine atoms on the dielectric constants, optoelectronic properties and charge carrier kinetic characteristics of indacenodithieno[3,2-b]thiophene based non-fullerene acceptors for efficient organic solar cells

In this work, the optical and electrochemical properties, charge mobility, the dielectric constants, photovoltaic performance of three non-fullerene acceptors (NFAs) named ITOR-IC, ITOR4F-IC, and ITOR-IC4F, in which 4-octyloxy-phenyl and 3-fluoro-4-octyloxy-phenyl side-chains were connected on the indacenodithieno[3,2-b]thiophene (IT) core and ended with 2-(3-oxo-indane-1-ylidene)-malononitrile or 2–3-(oxo-5,6-difluoro-indane-1-ylidene)-malononitrile end groups, were systematically investigated. It has been found that ITOR-IC4F which ended up with 2–3-(oxo-5,6-difluoro-indane-1-ylidene)-malononitrile groups, exhibited the narrowest bandgap and the highest dielectric constant of 5.10 as compared with that of ITOR-IC (4.03 at 1 kHz) and ITOR4F-IC (4.46 at 1 kHz). Moreover, the PM6:ITOR-IC4F based polymer solar cells (PSCs) presented the highest exciton dissociation probability, superior charge transport and extraction properties, combined with the longest carrier lifetime and the lowest recombination rate coefficient, eventually achieved the highest PCE of 11.1%. The results indicate that the introduction of fluorine atoms into end groups rather than side-chains of the NFAs is more conducive to increasing the dielectric constant of the IT-based NFA, more importantly, improving the photoresponse and the morphology of the active layer, thus devoting to the improvement of the light harvesting, exciton dissociation, as well as the carrier lifetime in the active layer. This work brings forward a new aspect to understand the influence of fluorine atoms substituent position on the properties of the NFAs for the further designation and optimization of new NFAs for efficient PSCs.

Experimental dielectronic recombination rate coefficients for lithium-like 40Ca17+

The rate coefficients for dielectronic recombination (DR) of lithium-like 40Ca17+ ions with ∆n = 0 core excitations are derived from electron–ion recombination spectra measured with merged-beams method at the heavy-ion storage ring CSRm. The experimental DR spectrum, in the electron–ion collision energy range of 0 to 42 eV in the center-of-mass frame, comprises of all DR resonance peaks belong to the 2s 2 S 1/2 → 2p 2 P 1/2, 3/2 core excitations. The resonant energies and strengths for the resolved resonances in 2pjnl series are determined by fitting of the measured DR peaks. The further interpretation of the measured DR rate coefficients has been performed by calculating the DR rate coefficients with relativistic configuration-interaction method implemented in flexible atomic code (FAC) and compared with the experimental results. The experimental results and FAC calculations are found to be in a good agreement within the experimental uncertainties. Moreover, temperature dependent plasma rate coefficients were constructed from 4 × 103 to 1 × 107 K energy region by convoluting experimental and theoretical DR rate coefficients with the Maxwellian energy distribution function and then compared with previously available data. The plasma DR rate coefficient is found to be significantly underestimated by the early theoretical data calculated by Jacobs et al, and Mazotta et al in the low temperature. In contrast, a very good agreement has been found between the theoretical DR data of Gu and Colgan et al and the presently measured results at the low temperature region. Therefore, the results in this work composed of a bench-mark data set for plasma modeling at the photoionized temperature range. We have also provided a fit to our measured and theoretical plasma rate coefficients for low temperature plasma modeling.

Calculations of electron-impact excitation and dielectronic recombination rate coefficients of highly charged silicon ions

The rate coefficients for dielectronic recombination and electron-impact excitation processes with H-like to Be-like silicon ions (${\mathrm{Si}}^{13+}\text{\ensuremath{-}}{\mathrm{Si}}^{10+}$) are calculated using relativistic distorted-wave approach. The prominent $▵n=1$ and the weaker $▵n=2$ and 3 dielectronic recombination (DR) resonances with $K$-shell excitations are presented, and compared with the existing DR experimental rate coefficients of ${\mathrm{Si}}^{13+}, {\mathrm{Si}}^{12+}$, and ${\mathrm{Si}}^{11+}$ ions, it is found that the theoretical DR rate coefficients are in very good agreement with the experimental results. With the same approach, the direct and resonant electron-impact excitation (EIE) cross sections associated with $1s\ensuremath{-}{n}^{\ensuremath{'}}{l}^{\ensuremath{'}}$ core excitations are calculated for the ground states of ${\mathrm{Si}}^{13+}\text{\ensuremath{-}}{\mathrm{Si}}^{10+}$ ions and found in excellent agreement with the available experiment. Finally, we present the synthesized DR and EIE rate coefficients for the sum of all detected $(13+\ensuremath{\sim}10+)$ charge states of Si and these agree well with the experimental results.

Photoejection from Various Systems and Radiative-Rate Coefficients

Photoionization or photodetachment is an important process. It has applications in solar- and astrophysics. In addition to accurate wave function of the target, accurate continuum functions are required. There are various approaches, like exchange approximation, method of polarized orbitals, close-coupling approximation, R-matrix formulation, exterior complex scaling, the recent hybrid theory, etc., to calculate scattering functions. We describe some of them used in calculations of photodetachment or photoabsorption cross sections of ions and atoms. Comparisons of cross sections obtained using different approaches for the ejected electron are given. Furthermore, recombination rate coefficients are also important in solar- and astrophysics and they have been calculated at various electron temperatures using the Maxwell velocity distribution function. Approaches based on the method of polarized orbitals do not provide any resonance structure of photoabsorption cross sections, in spite of the fact that accurate results have been obtained away from the resonance region and in the resonance region by calculating continuum functions to calculate resonance widths using phase shifts in the Breit–Wigner formula for calculating resonance parameters. Accurate resonance parameters in the elastic cross sections have been obtained using the hybrid theory and they compare well with those obtained using the Feshbach formulation. We conclude that accurate results for photoabsorption cross sections can be obtained using the hybrid theory.

Rate constants and molecular recombination pathways of oxygen from quasi-classical trajectory simulations of theO3system

• Investigation of recombination mechanisms using quasi-classical trajectory method. • Direct collisions are more effective for recombination. • Indirect recombinations proceed through orbiting pairs. • Recombination products result in strong non-Boltzmann internal energy distributions. • Recombination products exhibit large vibrational and low rotational quantum numbers. A lack of understanding of the dynamics of molecular recombination has led to the development of a large number of recombination models and methods to quantify recombination rate constants, each with their own set of assumptions and ranges of applicability. This work aims to unravel the complex dynamics behind the recombination of atomic oxygen to molecular oxygen using the quasi-classical trajectory method for the O 3 system. Recombination pathways considered include a single-step “direct” reaction, and a two-step mechanism that involves the formation of a long-lived intermediate which is stabilized through collision with a third body. The latter is further classified as Lindemann or Chaperon recombination pathways depending on the identity of the intermediate and the final product. The classical versions of all three mechanisms are explored in detail for the O 3 system. A time-lag parameter is introduced to quantify the time interval between the intermediate formation and third-body stabilization steps, and the direct collisions are treated as a limiting case when the time lag is zero. It is found that the recombination probabilities reduce as the time-lag is increased. Direct recombination events are dominated by head-on collisions, while the two step recombination events are characterized by a combination of glancing and head-on collisions. The resulting recombination products follow a strongly non-Boltzmann distribution. Recombination rate coefficients are computed through a novel rate coefficient formula that takes into consideration the Poisson distribution in time of third body stabilizing collisions with the orbiting pair characterized by finite lifetimes (on the order of picoseconds) that lead to recombination. Good agreement is obtained with recombination rates computed from detailed balance based on known dissociation rate coefficients. This approach thus enables the direct calculation of recombination rate coefficients at low temperatures, without the need for dissociation rate coefficients and detailed balance.

Asymmetric Lineshapes of Efimov Resonances in Mass-Imbalanced Ultracold Gases

The resonant profile of the rate coefficient for three-body recombination into a shallow dimer is investigated for mass-imbalanced systems. In the low-energy limit, three atoms collide with zero-range interactions, in a regime where the scattering lengths of the heavy–heavy and the heavy–light subsystems are positive and negative, respectively. For this physical system, the adiabatic hyperspherical representation is combined with a fully semi-classical method and we show that the shallow dimer recombination spectra display an asymmetric lineshape that originates from the coexistence of Efimov resonances with Stückelberg interference minima. These asymmetric lineshapes are quantified utilizing the Fano profile formula. In particular, a closed-form expression is derived that describes the width of the corresponding Efimov resonances and the Fano lineshape asymmetry parameter q. The profile of Efimov resonances exhibits a q-reversal effect as the inter- and intra-species scattering lengths vary. In the case of a diverging asymmetry parameter, i.e., |q|→∞, we show that the Efimov resonances possess zero width and are fully decoupled from the three-body and atom–dimer continua, and the corresponding Efimov metastable states behave as bound levels.

Photoionization and Electron-Ion Recombination of n = 1 to Very High n-Values of Hydrogenic Ions

Single electron hydrogen or hydrogenic ions have analytical forms to evaluate the atomic parameters for the inverse processes of photoionization and electron-ion recombination (H I + hν↔ H II + e) where H is hydrogen. Studies of these processes have continued until the present day (i) as the computations are restricted to lower principle quantum number n and (ii) to improve the accuracy. The analytical expressions have many terms and there are numerical instabilities arising from cancellations of terms. Strategies for fast convergence of contributions were developed but precise computations are still limited to lower n. This report gives a brief review of the earlier precise methodologies for hydrogen, and presents numerical tables of photoionization cross sections (σPI), and electron-ion recombination rate coefficients (αRC) obtained from recombination cross sections (σRC) for all n values going to a very high value of 800. σPI was obtained using the precise formalism of Burgess and Seaton, and Burgess. αRC was obtained through a finite integration that converge recombination exactly as implemented in the unified method of recombination of Nahar and Pradhan. Since the total electron-ion recombination includes all levels for n = 1–∞, the total asymptotic contribution of n = 801–∞, called the top-up, is obtained through a n−3 formula. A FORTRAN program “hpxrrc.f” is provided to compute photoionization cross sections, recombination cross sections and rate coefficients for any nl. The results on hydrogen atom can be used to obtain those for any hydrogenic ion of charge z through z-scaling relations provided in the theory section. The present results are of high precision and complete for astrophysical modelings.

TU16. BRAINXCAN IDENTIFIES BRAIN FEATURES ASSOCIATED WITH BEHAVIORAL AND PSYCHIATRIC TRAITS USING LARGE SCALE GENETIC AND IMAGING DATA

The recombination and dissociation of the resonantly stabilized 2-methylallyl radical has been studied in a diaphragmless shock tube by laser schlieren densitometry (LS) over temperatures of 700–1350 K and pressures of 60–260 Torr. Both 2,5-dimethyl-1,5-hexadiene and the new low temperature precursor 3-methylbut-3-enyl nitrite were used to generate 2-methylallyl radicals under these conditions. Rate coefficients were obtained for dissociation of the precursors, recombination of 2-methylallyl, and dissociation of 2-methylallyl by simulation of the LS profiles. The experiments are complemented by a priori theoretical calculations for both the recombination and dissociation of 2-methylallyl. The experimental results and theoretical predictions are in excellent agreement with one another. The calculated high pressure limit rate coefficient for recombination of 2-methylallyl is log(k1) = 14.737−0.641logT+251.39/(2.303×T) and that for dissociation of 2-methylallyl is log(k3) = 11.100−1.2295logT−28545/(2.303×T). The uncertainties in k1 and k3 are estimated as factors of 1.5. Rate coefficients are provided over a broad range of pressures for chemical kinetic modeling.

Nebular Emission from Lanthanide-rich Ejecta of Neutron Star Merger

Abstract The nebular phase of lanthanide-rich ejecta of a neutron star merger (NSM) is studied by using a one-zone model, in which the atomic properties are represented by a single species, neodymium (Nd). Under the assumption that β-decay of r-process nuclei is the heat and ionization source, we solve the ionization and thermal balance of the ejecta under non-local thermodynamic equilibrium. The atomic data including energy levels, radiative transition rates, collision strengths, and recombination rate coefficients, are obtained by using atomic structure codes, GRASP2K and HULLAC. We find that both permitted and forbidden lines roughly equally contribute to the cooling rate of Nd II and Nd III at the nebular temperatures. We show that the kinetic temperature and ionization degree increase with time in the early stage of the nebular phase while these quantities become approximately independent of time after the thermalization break of the heating rate because the processes relevant to the ionization and thermalization balance are attributed to two-body collision between electrons and ions at later times. As a result, in spite of the rapid decline of the luminosity, the shape of the emergent spectrum does not change significantly with time after the break. We show that the emission-line nebular spectrum of the pure Nd ejecta consists of a broad structure from 0.5 μm to 20 μm with two distinct peaks around 1 μm and 10 μm.

On the use of recombination rate coefficients in hydrogen transport calculations

The commonly accepted picture for the uptake of hydrogen isotopes (HIs) from the gas phase across the surface into a metal with an endothermic heat of solution for HIs is that of dissociation followed by thermalisation in a chemisorbed surface state and finally overcoming a surface barrier to enter the metal bulk where the HIs occupy interstitial solute sites. To leave the metal bulk the HIs first transition to the chemisorbed surface state from which they then enter gas phase by recombining into a diatomic molecule. This model is generally attributed to the work of Pick and Sonnenberg from 1985. They clearly distinguish surface states and subsurface solute sites where the recombination flux is proportional to the square of the concentration of chemisorbed atoms due the diatomic nature of this Langmuir–Hinshelwood process. In an effort to compare their extended model with an earlier surface model by Waelbroeck, which uses an expression for the recombination flux proportional to the square of the sub-surface interstitial solute concentration, they derive an effective recombination coefficient. However, also with the so-derived Pick and Sonnenberg recombination coefficient, the Waelbroeck model is only applicable under certain conditions. But, due to its simplicity, it is often used in boundary conditions of diffusion trapping type calculations, generally ignoring whether or not these conditions are met. This paper will use the full Pick and Sonnenberg model implemented in the TESSIM-X code and in simplified algebraic approximations, to show the limits of applicability of the Waelbroeck–Ansatz in modelling hydrogen transport in metals foreseen for the first wall of magnetic confinement fusion devices.

Dielectronic recombination in O4+ near the ionization threshold

Relativistic perturbation theory calculations are carried out for dielectronic recombination cross sections involving jj J levels near the ionization threshold. We included levels in the 1s 22p 23l, 1s 22s2p3l, 1s 22s2p4l, 1s 22s2p5l, and 1s 22s2p6l configurations of O3+ that lie within ±5.0 eV of the O4+ ionization threshold. Theoretical dielectronic recombination cross sections are compared with experimental dielectronic recombination rate coefficients from 0.0 eV to 5.0 eV above threshold.

Cavity ring-down spectroscopy study of neon assisted recombination of [formula omitted] ions with electrons

A stationary afterglow apparatus with Cavity Ring-Down spectrometer was combined with electron number density measurement system to study the third-body assisted recombination of H3+ ions with electrons in neon gas at the temperature of 110 K. The measured ternary recombination rate coefficient KNe(110K)=(1.8±0.2)×10-25cm6s-1 is close to that obtained in helium buffered plasma. The applicability of the present experimental setup for Einstein coefficients determination is also discussed.

Reactive collisions between electrons and BeT[formula omitted]: Complete set of thermal rate coefficients up to 5000 K

Rate coefficients for the dissociative recombination, vibrational excitation and vibrational de-excitation of the BeT+ ion for all vibrational levels of its ground electronic state (X1Σ+,vi+=0,…,27) are reported, including in the calculation the contribution of super-excited states of the BeT complex pertaining to three electronic symmetries - 2Π, 2Σ+, and 2Δ. These data are suitable for the kinetic modeling of beryllium and tritium containing plasma, as encountered in magnetic fusion devices with beryllium walls (JET, ITER). In the present study we restrict ourselves to incident electron energies from 10−3 up to 2.7eV, and to electron temperatures between 100 and 5000 K, respectively. Together with our earlier and closely related studies on the BeH+ and BeD+ systems, this present work completes the isotopic coverage for the beryllium monohydride ions. The vibrational energy (rather than the vibrational quantum state) is identified as a proper isotopic similarity parameter, e.g., for reduced but still isotopically correct plasma chemistry models.