Ar. Bandy et Jc. Ianni, STUDY OF THE HYDRATES OF H2SO4 USING DENSITY-FUNCTIONAL THEORY, The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory, 102(32), 1998, pp. 6533-6539
Density functional molecular orbital theory was used at the B3LYP/6-31
1++G(2d,2p)//B3LYP/6311++G(2d,2p) level of theory to study the hydrate
s of sulfuric acid (H2SO4. nH(2)O) for n = 0-7 and the dimer of the tr
ihydrate of sulfuric acid, (H2SO4. 3H(2)O)(2). Six neutrals of the fir
st six H2SO4. nH(2)O clusters (n = 1-6) were determined to be hydrogen
-bonded molecular complexes of H2SO4 and H2O and contain no H3O+ ions.
An H3O+ ion and HSO4- formed in clusters of H2SO4. nH(2)O for n = 3-7
. This is in contrast to the bulk phase where H2SO4 and two H2O's have
been converted to two H3O+ ions and a free SO42- ion. The energetics
of the hydration reactions also were obtained. The free energy of form
ation from free H2SO4 and H2O had a minimum at n = 3-4 at room tempera
ture. However, the free energy of formation of H2SO4. nH(2)O from free
H2SO4 and H2O decreased rapidly with temperature with the minimum bec
oming less pronounced and disappearing completely by 248 K. Below 248
K there is no free energy barrier to the formation of larger hydrates.