Thermodynamic characteristics of beryllium diiodide

sublimation and dimerization of beryllium diiodide were studied in the temp erature range from 537 to 570 K by the Knudsen effusion method in conjuncti on with a mass-spectrometric control of the vapor composition. The presence of the dimer (Be2I4) was for the first time detected in the saturated vapo r over crystalline beryllium diiodide. The enthalpies of sublimation Delta( s)H degrees(BeI2, 0 K) and formation Delta(f)H degrees(BeI2, g, 0 K) of the monomeric form of beryllium diiodide determined from the second law of the rmodynamics were found to be 126 +/- 5 and -65 +/- 9 kJ/mol, respectively. The enthalpies of sublimation and formation of Be,I, were also obtained for the first time: Delta(s)H degrees(Be2I4, g, 0 K) = 167 +/- 8 kJ/mol and De lta(f)H degrees(Be2I4, g, 0 K) = -215 +/- 18 kJ/mol. The enthalpy Delta(D)H degrees(Be2I4, g, 0 K) and entropy Delta(D)S degrees(Be2I4, g, 553 K) of d imerization of BeI2 were found to be -94 +/- 5 kJ/mol and -124 +/- 7 J/(mol K), respectively.