The values of ΔfG°T(Aln) (n = 3–10 atoms, T ≤ 3000 K), determined using the ROCBS-QB3 values of S°T(Aln) and of the corrected values of ΔfH°T(Aln)

Abstract

In the present work, the values of ΔfG°T(kAln)CORR have been determined on the basis of the thermochemistry of atomization reactions (ΔrG°T(kAln → n2Al) = ΔrH°T(kAln → n2Al) − TΔrS°T(kAln → n2Al)), calculated using the ROCBS-QB3 values of S°T(kAln) and corrected values of ΔfH°T(kAln)CORR as well as of the tabulated values of 2Al. The values of ΔfH°T(kAln)CORR have been determined using the temperature dependencies of ROCBS-QB3 values of ΔfH°T(kAln), calculated at T ≤ 3000 K, and the corrected values of ΔfH°298.15(kAln, 2 < n ≤ 10 atoms)CORR, determined using the perfect linear correlation dependence, proposed in the present work for the clusters Xm (m ≤ 8 atoms), formed by the elements of the third row of the periodic table of elements (X = Na, Mg, Si, S, P and Cl, m ≥ 2 atoms).The values of ΔfH°298.15(kAln, 2 < n ≤ 10 atoms)CORR and ΔfH°0(kAln, 2 < n ≤ 10 atoms)CORR have been in good agreement, respectively, with the values of ΔfH°298.15(kAln, 2 < n ≤ 10 atoms), determined using the ROCBS-QB3 and CBS-Q thermochemistry of isodesmic and non isodesmic reactions, as well as with the theoretical values of the cohesive energies, reported previously. The CBS-Q and CBS-QB3 approaches have not been used for the calculations of the values of ΔfH°T(kAln, 2 < n ≤ 10 atoms) due to the spin contamination problems.At the same time, the effect of the spin contamination on the values of S°298.15(Xm) has not been significant, and has not been expected for the values of S°298.15(kAln). The values of S°298.15(Xm) and S°298.15(kAln), calculated using the different QM approaches (CBS-Q, RO/CBS-QB3, LSDA, PBEPBE, MP2) have been in the agreement each with the others. However, the more consistent values of S°298.15(kAln) have been determined using the correlation dependencies between the tabulated and calculated values of S°298.15(Xm).The values of ΔfG°T(kAln, n > 4 atoms), calculated in the present work, have been up to 250 kJ/mol higher those theoretical values, reported previously. The corresponding values of equilibrium constants (K°p)n−1 of reactions kAln = 2Al + k±1Aln−1 (n > 3 atoms) indicate that the contribution of the kAln clusters to the gas phase oxidation of 2Al is insignificant.