The γ-Radiolysis of Ethane. III. The Effect of Density on Ion Scavenging Reactions above the Critical Temperature

Abstract

The radiolysis of ethane has been studied over the density range 0.0018-0.5 g cc-' at a temperature just above the critical point. The variations of product yields with increasing density are consistent with increasing collisional stabilization of excited species. Electron scavenging by sulfurhexafluoride in ethane at 0.275 g cc-I is accurately described by an expression used for liquid phase scavenging with G,,,, ,.., = 0.65. At 0.052 g cc-I a much higher yield of free ions is observed and at high sulfurhexafluoride concentrations there is a sensitized decomposition of ethane.Ammonia-d, scavenges ions at all densities but in the region around 0.07 g cc-' a mechanism operates which produces more than one hydrogen molecule per ion scavenged. The freely diffusing ions d o not appear to be readily scavenged by ammonia-d3.La radiolyse de ]'ethane a ttC CtudiCe dans l'intervalle de densit6 0.00184.5 g cc-', a une temperature juste au dessus celle du point critique. Les variations des rendernents en produit lorsque la densit6 augmente sont cohCrentes avec I'accroissement de la stabilisation par choc des espkes excitees. Le pitgeage des Clectrons par l'hexafluorure de soufre dans I'ethane a la densite 0.275 g cc-' est dCcrit avec prCcision par une expression utilisee pour le pitgeage en phase liquide avec GI,,, = 0.65. Pour une densite de 0.52 g cc-' on observe un plus grand rendement en ions libres et pour des concentrations Clevtes en hexafluorure de soufre on note une dCcomposition sensible de Ethane.

The effect of reactant purity on the radiolysis of gaseous ethane and propane

“…it cannot compete effectively with condensation reaction 6 under our experiinental conditions k6 z 10-1° cc molecule-' s-l (16) Diineric ion formed in reaction 6 is unreactive towards ethane (16), its structure and heat of formation are unknown, either a chemical bond is formed between the ion and the molecule or the link is due to attractive physical forces. If the !atter case is true, the occurrence of reaction 7 may be assumed.…”

Fission Fragment Radiolysis in Ethane-Ammonia System

“…In n-butane formation, no significant effect of FF can be expected from the predominance of reaction ( 2) over reaction ( 9 ).…”

“…The fastest second-order reaction should be a neutralization reaction, such as that between C 2 H 6 + and electrons : ( 9) In order to let the effects of FF irradiation make itself felt, the rate of reaction ( 9) must be faster than the proton transfer reaction ( 2) in the FF tracks. To estimate the competition between the reactions ( 2) and ( 9 ), the concentration of C 2 H 6 +, and the rates of the reactions ( 2) and ( 9) in an FF track was estimated in the following manner.…”

“…This permits the rates of reactions ( 2) and ( 9) to be estimated with appropriate values assumed for the rate constants of these reactions, the result being as shown in Table 2. As the rate constant for reaction ( 9 ), the value adopted was that generally accepted for the neutralization reaction in the gas phase : k 9 "-'5 X 10-7 cm 3 /molecule· sec< 15 J. The corresponding value for reaction ( 2) was k 2 "-'5 x 10-• cm 3 /molecule•sec, estimated from analogous reactions< 2 J<Is).…”

Fission Fragment Radiolysis in Ethane-Ammonia System

“…In the FF tracks, it should appear reasonable to consider the occurrence of secondorder reactions with respect to the active species. The fastest second-order reaction should be a neutralization reaction, such as that between C 2 H 6 + and electrons : ( 9) In order to let the effects of FF irradiation make itself felt, the rate of reaction ( 9) must be faster than the proton transfer reaction ( 2) in the FF tracks. To estimate the competition between the reactions ( 2) and ( 9 ), the concentration of C 2 H 6 +, and the rates of the reactions ( 2) and ( 9) in an FF track was estimated in the following manner.…”