Mass Spectrometric Study of Thermolysis Mechanism of Metal Acetylacetonates Vapour

Abstract
The processes of thermal decomposition of aluminium(III) and scandium(III) acetylacetonates (Al(aa)₃ and Sc(aa)₃) were investigated in the 160-650°C temperature range using a high-temperature molecular beam source with mass spectrometric sampling of the gas phase composition directly at the outlet from the reaction zone. A scheme of thermal decomposition of aluminium(III) and scandium(III) acetylacetonates vapour is suggested. It is established that the common mechanism of thermolysis of these complexes is due to the commonness of electronic structure of ions Mg²⁺, Al³⁺, Sc³⁺ and Hf⁴⁺. According to the scheme, the process proceeds along three parallel routes, one of them being possible only for complexes possessing more than two ligands ; in this case the gaseous products resulting from cyclic dimerization of ligand fragments are formed. The influence of oxygen and hydrogen on the composition of the gaseous products and the mechanism of thermolysis of the complexes vapour are also established. From temperature curves, the effective values of kinetic parameters in Arrhenius equation are calculated for the first order reaction.