Detection of the plastic-crystalline transition of trioxane by positron annihilation lifetime spectroscopy

Abstract

The plastic-crystalline transition and the melting temperature of trioxane have been detected at ca. 50 and 64 °C, respectively, by positron annihilation lifetime spectroscopy. Changes in the ortho-positronium parameters, τ₃ and I₃, are correlated with the fluctuations occurring in the mean size and density, respectively, of the free volume of trioxane during the solid–solid transition. Large variations in the mean free volume were detected at the plastic-crystalline transition.