Effect of Electric Field Strength on the Free Ion Yields in the X-Radiolysis of Liquids: Influence of Molecular Structure and Temperature

Free ion yields G: were measured at electric field strengths E up to 6.7 MV m-' in liquid isobutane at 556 5 d / k g m-' 5 739 (294.4-1 14.6 K). The yields decreased with decreasing temperature and increasing density up to 677 kg m-'; further increases in density led to little change in G:. The thermalization distance distribution F ( y ) was estimated by fitting the field dependence of G: using the extended Onsager model. At lower densities F ( y ) = YGP (three-dimensional Gaussian body with power tail) provided an adequate fit to the results, while at higher densities F ( y ) = YE (onedimensional exponential distribution) was better. Thus the electron-scattering properties of liquid isobutane change somewhat with density. The thermalizing ability of liquid isobutane increased with increasing density up to -660 kg m-), then decreased at densities >690 kg m-? By comparison, the Arrhenius temperature coefficient of mobility of thermal electrons changed in the same density region: E , = 7 kJ mol-' at d < 660 kg m-', and = I 6 kJ mol-' at d > 690 kg -3 Key words: isobutane, electron thermalization distance, free ion yield, liquid, electron mobility, radiolysis.TAKEHISA YOSHINARI, NORMAN GEE et GORDON R . FREEMAN. Can. J. Chem. 70, 327 (1992) Operant dans de I'isobutane liquide a 556 5 d/kg m-' 5 739 (de 294.4 K a 114.6 K), on a mesure les rendements en ions libres G: a des forces de champ Clectrique E allant jusqu'a 6.7 MV m-'. Les rendements diminuent lorsque la temptrature diminue et lorsque la densit6 augmente jusqu'a 677 kg une augmentation plus poussCe de la densitt affecte tres Itgkrement la valeur du G:. On a CvaluC la distribution de la distance de thermalisation F ( y ) en ajustant I'influence du champ sur la valeur du G: en faisant appel au modele Ctendu de Onsager. Pour des densites plus faibles, ]'equation F ( y ) = YGP (corps gaussien tridimensionnel et queue avec des puissances) permet d'obtenir une concordance adequate avec les resultats; par ailleurs, pour des densites plus ClevCes, I'Cquation F ( y ) = YE (distribution exponentielle unidimensionnelle) est meilleure. Les propriCtCs de dispersion des klectrons par I'isobutane liquide varient donc un peu avec la densitC. Lorsque la densite augmente jusqu'a environ 660 kg m-3, la capacitC de thermalisation de I'isobutane liquide augmente d'une fason parallkle; ?I des densites >690 kg m-" cette capacite commence B diminuer. Par comparaison, le coefficient de temperature d'ArrhCnius pour la mobilite des Clectrons thermiques change aussi dans cette mCme region de densite : E, = 7 kJ mol-' ?I d < 660 kg m-', et E, = 16 kJ mol-' d > 690 kg/m3.

Section: M' Cathodesupporting

confidence: 63%

“…[6], where 1 is the distance between the parallel electrodes and V is the applied voltage. For the conditions of this work the diffusion correction (1 1) was negligible.…”

Section: Electron Mobilitymentioning

confidence: 99%

Electron thermalization distance distributions and thermal electron mobilities in dense liquid isobutane

Yoshinari¹,

Gee²,

Freeman³

1992

“…The first one is based on the random walk inode1 (22) and is a three dimensional Gaussian (8,23,24). We will call it YG.…”

Section: The Modelmentioning

confidence: 99%

Low energy electron ranges in liquids: determination by nonhomogeneous kinetics

Dodelet¹

1977

Self Cite

J.-P. DODELET. Can. J. Chem. 55. 2050Chem. 55. (1977. Free ion yields have been measured in four hydrocarbon liquids: 71-pentane, cyclopentane, neopentane, and neohexane. Each liquid has been studied from room temperature or below up to the critical temperature. Theoretical curves have been calculated using the relation between the free ion yields and the external field strength derived by Terlecki and Fiutak on the basis of an equation by Onsager. Two popular electron range distribution functions, Gaussian and exponential, have been shown not to be an adequate representation of the reality as far as the model used for the calculations is concerned. In order to fit experimental points, both range distribution functions would require a drastic increase in the total ionization yield, GI,,, with temperature increase. This would mean an unrealistic decrease of the ionization potential of the molecule from the melting point up to the critical temperature.It is possible to keep GI,, quite constant and within the range of values obtained by other techniques by extending the Gaussian range distribution function with a (range)-3 probability tail. The most probable range can be normalized for the liquid density. This parameter has been used to obtain information a b o~~t the behaviour of epithermal electrons in the four alkane liquids from the melting point up to the critical temperature.( I ) Normalized penetration ranges of epithermal electrons are dependent on the structure of the molecule in the entire liquid range but differences are smaller at critical than at low temperatures.(2) Normalized penetration ranges of epithermal electrons pass through a maximum in the liquid phase for neopentane, neohexane, and cyclopentane. No maximum is observed for n-pentane.(3) There is no drastic change in the behaviour of epithermal electrons in these alkanes at t h e critical temperature.J.-P. DODELET. Can. J. Chem. 55.2050Chem. 55. (1977. Les rendements en ions libres ont Cte mesurks dans quatre hydrocarbures liquides: le npentane, le cyclopentane, le neopentane et le nCohexane. Chaque hydrocarbure a ete etudie depuis une temperature egale ou infkrieure a celle du laboratoire jusqu'a la temperature critique. Les courbes thtoriques ont et6 calculCes en utilisant la relation, dtduite par Terlecki et Fiutak d'apres une equation d'onsager, entre les rendements en ions libres et le champ Clectrique applique. Deux distributions des parcours electroniques, I'une de type gaussien, I'autre exponentiel, trks populaires dans la litterature, ont ete utilisees dans les calculs et n'ont pas donne satisfaction dans le cadre de ce modele. En effet, pour ces deux distributions, une bonne coincidence entre les calculs et l'experience requerrait, lorsque la temperature augmentait un accroissement considerable du rendement total en ions, GI,,, ce qui aurait signifie une diminution constante, tres peu probable, du potentiel d'ionisation de la molecule a partir du point de fusion jusqu'a la temperature critique. I1 est possible de maintenir GI,,, r...

“…f(t)dt represents the fraction that undergoes neutralization between t and t + dt. The fraction of ion pairs, F(t), which exists at any time t after an instantaneous pulse irradiation can be determined simply by integrating f(t) over all values greater than t Although hitherto numerous forms of f(r) have been compared and tested against experimentally observed behaviors of electrons in liquid hydrocarbons (5,9,10,17), no single form has yet been established as the universally satisfactory f(r) (10). Since no such test has been performed in dense gases, we choose a single parameter Gaussian, [3], and a simple exponential function, [6], in the calculation mainly on grounds of their simple forms and of the fact that both forms have been shown to give an adequate description of experimental results under some restriction in the range of applicability (9, lo), which appears to fit the present case (1 1).…”

Section: Lifetime Distribution Functionsmentioning

confidence: 99%

Geminate Recombination of Ion Pairs In The Radiolysis of Dense Hydrocarbon Gases

Nishikawa¹

1975

MASARU NISHIKAWA. Can. J. Chem. 53, 3075 (1975). The distribution functions of ion-electron pair separation distances in irradiated hydrocarbon gases are transformed into those of neutralization times by means of the r 3 rule of time-distance obtained under the approximation that Coulomb field predominates in their mutual diffusion. In this approximation lifetime distribution is a function-of (3DrC)'l3/b, where D is the total diffusion constant, D+ + D,, r, is the Onsager distance, and b is the characteristic distance of the respective spat~al distribution function. Using the values of parameters previously estimated for supercritical hydrocarbons, it was found that for butanes the lifetime in the gas phase at density ~0 . 4 g/ml is shorter than that in the liquid phase at room temperature.MASARU NISHIKAWA. Can. J. Chem. 53, 3075 (1975).On transforme les fonctions de distribution des distances de skparation ion-paire d'klectron dans des hydrocarbures gaseux irradiks en fonction de temps de neutralisation a I'aide de la regle en r 3 du temps us. distance lorsque I'on fait I'approximation que le champ de Coulomb prkdomine lors de leur diffusion mutuelle. Dans cette approximation, la distribution des durks de vie est une fonction de (3 Drc)'13/b oh D est la constante totale de diffusion, D+ + D,, r, est la distance de Onsager et b la distance caractkristique des fonctions respectives de distribution spaciale. Utilisant les valeurs de parametres obtenues antkrieurement pour des hydrocarbures supercritiques, on a trouvk pour les butanes que la durke de vie en phase gaseuse a densitk d'environ 0.4 g/ml est plus courte que celle en phase liquide i tempkrature de la piece.[Traduit par le journal]The lifetime distribution of the electron produced in a medium by irradiation with respect to neutralization has been the subject of numerous theoretical studies, in which several different approaches have been used (1-6, 12). In one approach the evolution of neutralization is described by the Smoluchowski equation, which is then solved either under 'the prescribed diffusion' approximation (I), numerically (2), with analog computer (3), or by Laplace transform method (4). In another approach the motion of electrons is approximated by their drift motion in the Coulomb field of ions (forced diffusion approximation), where the distribution of neutralization times is generated by the distribution of ionelectron separation distances (5, 6). The results obtained along with these and other approaches give rise to different forms of the distribution, but the experimental data to compare with them are rather limited at the present time. However, the comparison of both approximations made by 'Partially supported by the Grant in Aid from the Ministry of Education. Dodelet and Freeman ( 9 , and a recent success of the latter approximation in describing the observed neutralization in liquid propane (6) seem to indicate the usefulness of the forced diffusion approximation.The objective of the present calculation is to find out semiquantitativ...