A density functional study of the hydration energies and proton affinitiesof some scandium compounds with hydrogen and oxygen

The hydration energies of four basic ions Sc+, ScO+, ScOH+ and Sc(OH)(2)(+) , and proton affinities for various neutral Sc species, which might exist i n flames doped with Sc, were studied with density functional methods. Two f unctionals, B3LYP and BP86, equipped with two basis sets, TZVP and 6-311 + G(3df,3pd), were employed. The geometries and frequencies from the four m ethods are very similar. The hydration energies from the four methods diffe r by 0-13 kcal/mol because the functional effect and the basis set effect b ehave very differently for H2O and the Sc species. With our preferred A2 me thod B3LYP/6-311 + + G(3df,3pd), the theoretical hydration energy is simila r to 37 kcal/mol for monohydrates, similar to 68 kcal/mol for dihydrates an d similar to 101 kcal/mol for trihydrates at 298.15 K. The proton affinitie s for most scandium species (200-250 kcal/mol) such as Se, ScO, ScOH, HScO, OScO, OScOH, Sc(OH)(2) and Sc(OH)(3) are much higher than the proton affin ity of H2O (165.2 kcal/mol). These results indicate that chemical ionisatio n by proton transfer may play an important role for ionisation in flames do ped with Sc. (C) 2001 Elsevier Science B.V. All rights reserved.