Recombination coefficient

A device model to describe two-carrier structures is basically similar to that used for one carrier structures except that continuity equations for both earner types are solved. The additional process that must be considered is charge carrier recombination. The recombination is bimolecular, R=y(np), where the recombination coefficient is given by 43)... 

In these particular experiments it proved impossible to investigate the effect of copper concentration on the catalytic activity of alloys free of the hydride phase. Figure 10 69, 64a, 65) illustrates the changing values of the recombination coefficient on nickel-copper alloys related to the composition of the alloy at room temperature. The small amount of copper introduced into the nickel already distinctly decreased the catalytic ac-... 

Thus nickel and nickel-copper alloy films evaporated in vacuo onto the inner walls of the reaction vessel have been chosen for further investigations. The films were deposited onto the inner wall of a glass tube kept at 450°C their thickness amounted to approximately 2000 A. After annealing at the same temperature in vacuo they were transferred into the side-arm of the Smith-Linnett apparatus in order for the recombination coefficients to be determined. The bulk homogeneity of alloy films prepared in this way was confirmed by X-ray diffraction (65, 65a, 66). 

I is the number of ions created per unit volume and time. The value used was / = 1.4 X 1010 ions cc.-1 sec.-1 which corresponds to irradiation with a 50-mc. source (see section on intensity of irradiation above) n is the number of ions per cc. Ion recombination coefficient... 

H30 + and are not lost by diffusion or recombination. If they were lost by dissociative recombination, the recombination coefficient would have to be too large a > 3 X 10-6 cm.3 molecule-1 sec.-1 would be required. 

In addition to measuring total recombination coefficients, experimentalists seek to determine absolute or relative yields of specific recombination products by emission spectroscopy, laser induced fluorescence, and optical absorption. In most such measurements, the products suffer many collisions between their creation and detection and nothing can be deduced about their initial translational energies. Limited, but important, information on the kinetic energies of the nascent products can be obtained by examination of the widths of emitted spectral lines and by... 

Thus, collisional-radiative recombination will not make an important contribution to the deionization in typical low-density afterglow experiments, except in cases where dissociative recombination is extremely slow, e.g. for He . However, collisional-radiative recombination may not be slow compared to the partial dissociative recombination coefficient for a particular product branch. For instance, a product channel that accounts for only 1% of the total may very well arise from collisional-radiative recombination. 

One resolution of the problem that gained acceptance for a while was proposed by Adams et al.18 In their flowing afterglow measurements, the apparent recombination coefficient of fell off to a small value in the late afterglow . This finding... 

A careful repeat of the flowing-afterglow measurement of Adams et al. 18 was subsequently carried out by Smith and Spanel.29 The results confirmed the Adams et al. observation that the recombination coefficient appears to fall off to a small value in the late afterglow. The authors concluded that the small recombination coefficient observed in the late afterglow is the proper value for v = 0 ions and that the initial rapid plasma decay in the early afterglow should be ascribed to vibrationally excited ions. 

Gougousi et al. first attempted to explain their findings by assuming the presence of Hj ions in two vibrational states (v = 0 and v, = 1) with two different recombination coefficients, and quenching of the v, = 1 ions by H2. This two-state model did not produce a consistent, quantitative fit to the data and this interpretation was abandoned. 

The afterglow data for Ne, 60 ArJ,61 Kr, 62 and Xe2 63 showed that the total recombination coefficients, as determined from the decay of the electron density, were sensibly independent of the gas pressure. Typically, the pressure was varied by at least a factor of 3 and no systematic variation of the total recombination coefficient was found. The observed plasma decay was compatible with the assumption that the total recombination coefficients are independent of the electron density (in the range from approximately 109 to 1010 cm-3). 

Numerous visible atomic spectral lines were observed during the afterglow. The decay of the intensities of these lines followed approximately the n7 dependence that is expected for lines produced by recombination. However, the absolute intensities of the lines were not measured and no partial recombination coefficients were obtained. Since only a limited spectral range was examined, many lines that might be expected to come from recombination were therefore not observed. 

Our discussion of complex formation in electron-ion recombination, field effects, and three-body recombination has perhaps posed more questions than it has answered. In the case of H3 recombination, the experimental observations suggest but do not prove that complex formation is an important mechanism. Three-body recombination involving complex formation is not likely to have much effect on the total recombination coefficients of diatomic ions, but it may alter the yield of minor product channels. Complex formation may be most prevalent in the case of large polyatomic ions, but there is a serious lack of experimental data and theoretical calculations that can be adduced for or against complex formation. 

Mean Life, Attachment, Recombination and Plateout. The approximate mean life (T) of Po-218 in ion form can be represented as ( X + an + N + po) where X is the decay constant for Po-218, a is the recombination coefficient for Po-218 and ordinary ions of negative charge in the atmosphere, n is the concentration of small negative ions, 8 is the attachment coefficient, N is the number of condensation... 

Temperature gradients and local temperature fluctuations usually parameterized by t2 (Peimbert 1967) lead to a systematic bias when the electron temperature determined conventionally from [O m] X 4363/a 5007 is substituted into the expressions for effective recombination coefficients of hydrogen and helium. 

Bimodal polymer, 20 165 Bimodal polymerization, 20 531 Bimodal reactor technology, for high density polyethylene, 20 170 Bimodal weight ratio, 70 17 Bimolecular reaction, 74 625 Bimolecular recombination coefficient, 74 833... 

First a rough approach. Take a one-step process with generation and recombination coefficients g(n), r(n) as in (VI.5.1). Its macroscopic equation... 

The results in Figure 1 imply that the abundance of chemiions initially present in the exhaust is 109/cm3. As noted by Yu and Turco [75], this number is consistent with the measurement of charge concentrations in flames, and with known ion-ion recombination coefficients, when the time scale of the exhaust emission into the atmosphere is taken into account. More recently, direct sampling of massive ion clusters (greater than 9500 amu) in fresh jet exhaust confirms that the chemiion concentration near the exit plane is of the order of 109/cm3 [90-92]. 

Fig. 14. Dependence of log10 on bulk composition for Pd-Ag and Ni-Cu alloys. yH is the recombination coefficient of hydrogen atoms. From Hardy and Linnett (26).

A. Burgess, A general formula for the estimation of dielectronic recombination coefficients in low-density plasmas, Astrophys. J. 141 (1965) 1588. 

When an electron neutralizes a positive ion, the energy released can be dissipated either in photon emission (radiative recombination), or by a third body encounter with the transient excited atom or molecule (three-body recombination) or by the fragmentation of the transient excited molecule (dissociative recombination). Radiative recombination only occurs with a very small probability and three-body recombination only occurs at high pressures or high charge densities, neither of these being appropriate to the atmospheric plasma. It is the dissociative process, exemplified by reactions (5a) and (5b), which is dominant in the ionosphere. In fact, reactions (5a) and (5b) are almost entirely responsible for the loss of ionization in the ionosphere above 85 km altitude (with N2 recombination contributing somewhat) as is readily shown by simple calculations based on laboratory determinations of dissociative recombination coefficients, are, for the dominant molecular ions 02 and NO+. 

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