Research Article published by Cogent OA
The properties of trimer Cs3X3 and tetramer Cs4X4 (X = Br, I) molecules
have been studied using DFT with B3LYP5 functional and MP2 and MP4 methods.
Two equilibrium geometrical structures of trimers, hexagonal (D3 h) and “butterflyshaped”
(Cs), and one for tetramers, distorted cubic (Td), are confirmed to exist;
geometrical parameters and vibrational spectra are determined. The relative
concentration of Cs3X3 isomers has been evaluated; the butterfly-shaped isomer
dominates over hexagonal in saturated vapour in a broad temperature range. The
dissociation reactions through different channels have been considered and enthalpies
of formation ΔfH°(0) of clusters determined:−858 ± 20 kJ mol−1 (Cs3Br3),
−698 ± 20 kJ mol−1 (Cs3I3), −1270 ± 30 kJ mol−1 (Cs4Br4) and −1045 ± 30 kJ mol−1
(Cs4I4). The Gibbs free energies ΔrG°(T) calculated for the dissociation reactions of
trimer and tetramer molecules have indicated that these molecules are resistive in
narrow temperature range only and decompose spontaneously with temperature
increase with elimination of dimer molecules.