On the probability of positronium formation in liquid molecular substances—An improvement of the spur model

Abstract

An idea about influence of excited molecules on positronium (Ps) formation is proposed: In addition to the excess electrons, excited molecules created in e + spur can also promote the formation of Ps. The excited molecule reaction may exert an influence on the probability of Ps formation by way of the quenching of excited energy or transfer of electron from excited molecule to additive. According to the competitive reaction mechanism in the spur, some functions correlating the probability of o-Ps formation ( I 3) with additive concentration are derived from binary systems. By these equations some theoretical fittings are made for some mixtures in which a certain additive such as CS 2, SF 6, C 2H 5Br, CCl 4 or C 6F 6 is included. From the fitting parameters, some valuable information about affinity of additive and ionization potential of excited molecule is obtained. For example, some electron affinities are already known: E a ( SF 6) = 1.48 eV, E a ( CCl 4) = 2.12 eV, E a ( CS 2) = 1.13 eV, then we can obtain E a(C 2H 5Br) = 1.30 eV, I(iso-C 8H 18) = 1.22 eV, I(TMS ∗) is in 1.30 eV ∼ 2.12 eV, and so on. Furthermore some “knotty problems” in positronium chemistry are interpreted satisfactorily.