Molecular Orbital Study of Proton Transfer in (H3NHOH2)+
The Journal of Physical Chemistry
American Chemical Society
Ab initio molecular orbital methods are used to study transfer of the central proton in the asymmetric (H3NHOH2)+ system. Calculations are performed at the Hartree-Fock level with basis sets of split-valence (4-31G) and double-�� plus polarization function (DZP) quality. The effects of electron correlation upon the transfer potentials are computed via the generalized valence bond (GVB) and polarization configuration interaction (POL-CI) techniques. The barrier to proton transfer between NH3 and OH2 is observed to heighten as the distance between the latter two molecules is increased. At the equilibrium R(N0) hydrogen-bond length, the transfer potential contains a single minimum, (H3NH...OH2)+, in which the central proton is more closely associated with NH3. In both the rapid and adiabatic models of proton transfer, there is no energy barrier to decay of (H3N...HOH2)+ to the equilibrium (H3NH...OH2)+ structure. While all the calculations agree on the above points, there are some notable quantitative discrepancies between the various methods. Enlargement of the basis set at the Hartree-Fock level results in higher transfer barriers while subsequent inclusion of electron correlation (POL-CI) leads to barrier reductions. The GVB procedure, with its partial treatment of correlation, produces changes in the potentials opposite to those observed for the more complete POL-CI treatment.
Molecular Orbital Study of Proton Transfer in (H3NHOH2)+ S. Scheiner and L. B. Harding J. Phys. Chem., 1983 87 (7), 1145-1153.