The thermodynamic properties of the gaseous dimer of CdI2

Abstract

The vaporization of CdI2(s) was investigated in the temperature range between 534 and 613 K by the Knudsen effusion mass spectrometry. The Cd2I4(g)-dimer content in the equilibrium vapor of CdI2(s) was determined for the first time. The enthalpies of sublimation and dissociation of Cd2I4(g) were evaluated according to the third-law method using the experimental p(CdI2)/p(Cd2I4) ratio. Molecular parameters and the thermodynamic functions of Cd2I4(g) were determined theoretically. Enthalpy of sublimation, 2 CdI2(s)=Cd2I4(g), was obtained as: ΔsubH0(298.15 K)=222.5±6.2 kJ mol−1, and enthalpy of dissociation, Cd2I4(g)=2 CdI2(g), was determined as ΔdH0(298.15 K)=70.7±7.0 kJ mol−1. The standard enthalpy of formation of Cd2I4(g) was obtained as ΔfH0(298.15 K)=−188.1±6.3 kJ mol−1.