A molecular basis of the bubble model of positronium annihilation in liquids

The bubble model of positronium annihilation in liquids universally used for the description of positron annihilation in liquids involves macroscopic notions, based on a continuum description of the liquid (such as surface tension extended to nano-particle dimensions), which is somewhat unsatisfactory. An elementary molecular level description is presented. The consequent clarification of underlying concepts (such as the location of the surface of tension) is injected into the bubble model to obtain a modified version. It is shown that there is a considerable difference between the effective surface tension in such microbubbles and the corresponding bulk values The concept of a work function for the positronium in the liquid is introduced on the basis of this model from which some conclusions are drawn regarding the quasi-positronium, the precursor of the positronium in the bubble, as being a rather extended delocalized entity. (C) 2002 Elsevier Science B.V. All rights reserved.