Upper panel: TE abundances of the abundant molecules CO, CO₂, H₂O (black), OH, and O₂ as a function of temperature for different C/O ratios. Middle panel: TE abundances of the aluminium-bearing molecules AlO, AlOH, Al₂O, and AlO₂ as well as Al and Al⁺, as a function of temperature for different C/O ratios. Lower panel: TE abundances of the aluminium-bearing clusters OAlOH, Al(OH)₂, Al₃O₃, Al₄O₄, Al₄O₅, Al₄O₆, and AlSiO₃, which participate in the formation of the alumina dimer (Al₄O₆), as a function of temperature for different C/O ratios. Straight lines correspond to C/O = 0.4, dashed lines to C/O = 0.7, and dashed-dotted line to C/O = 1.0, respectively. The pressure is kept constant at 10⁻⁵ bar.