Self-trapping at the liquid-vapor critical point

Experiments suggest that localization via self-trapping plays a central role in the behavior of equilibrated low mass particles in both liquids and in supercritical fluids. In the latter case, the behavior is dominated by the liquid-vapor critical point which is difficult to probe, both experimentally and theoretically. Here, for the first time, we present the results of path-integral computations of the characteristics of a self-trapped particle at the critical point of a Lennard-Jones fluid for a positive particle-atom scattering length. We investigate the influence of the range of the particle-atom interaction on trapping properties, and the pick-off decay rate for the case where the particle is orthopositronium. We find that, at the critical point, the transition from the self-trapped inhomogeneity to the density of the surrounding fluid is more gradual than in the liquid, or dense gas, away from the critical point. In addition the "shell structure" in fluid density surrounding the droplet is effaced.