Effect of CCl₄ on positronium formation in isooctane

Abstract

The effect of CCl₄ on positronium (Ps) formation is examined in isooctane through positron lifetime spectroscopy experiments, in the framework of a series of studies on AOT-based reverse micellar systems. This solute appears as a rather strong Ps formation inhibitor, as expected in view of its well-known electron scavenging properties. The reciprocal of the triplet Ps intensity (1/I ₃) varies linearly with CCl₄ concentration (C), up to about 0.08M, allowing to derive a high inhibition constant,k=36.6M⁻¹. Above 0.08M, however, the inhibition slackens out, which is attributed to an anti-inhibition effect. On the basis of previous reports on halocompounds, a general scheme of reactions is proposed to occur in the positron spur, including, besides the primary Ps formation through thee ⁺/e⁻ reaction and the recombination reactions, electron scavenging by CCl₄ as the direct inhibiting reaction, followed by the reaction of the thus formed anion with the positron. The latter reaction may lead either to a [CCl₄Ps] bound-state or, if the positron picks off the electron from the anion, to some additional Ps formation. By using a simple quantitative approach to this scheme, an equation descriptive of the variation ofI ₃ withC is derived which agrees well with the experimental data.