Structural, vibrational and thermodynamic properties of the isomers of the dimer molecules Ba2X4 (X = F, Cl, Br, or I)

Geometrical parameters and vibrational spectra of the dimer Ba2X4 molecules were calculated; different isomeric structures were revealed. For the Ba2F4, Ba2Cl4, and Ba2Br4, three isomers of C-3v, C-2v, and C-2h symmetries were confirmed to exist while for Ba2I4 only two isomers, C-3v and C-2h, were confirmed. For all halides, the bipyramidal C-3v isomers possessed the lowest energy. The structural parameters and vibrational frequencies were employed in calculation of thermodynamic functions and enthalpies of dissociation reactions of the species. The enthalpies of formation increment H-f(0) of the C-3v isomers were obtained (in kJ mol(-1)): - 1874 +/- 2 (Ba2F4); - 1236 +/- 7 (Ba2Cl4); - 1023 +/- 8 (Ba2Br4); - 787 +/- 11 (Ba2I4). The relative abundance of the isomeric forms was evaluated for a broad temperature range, between 200 and 2000 K. It was shown that the concentrations of different isomers appeared to be comparable in saturated vapors at temperatures close to experimental conditions.