Ab initio studies of the hydrated H/sub 3/O/sup +/ ion. II. The energetics of proton motion in higher hydrates (n=3--5)
Ab initio molecular orbital calculations on the higher hydrates of H/sub 3/O/sup +/, using a split valence level basis set (4--31G), have led to the following results. (1) Energies for successive hydration are in good accord with gas-phase thermochemical data. (2) Hydrogen-bonded OH and OxxxO distances in H/sub 9/O/sub 4//sup +/ are in excellent agreement with condensed phase diffraction data. (3) Large variations in OH (9 or approx. =0.08 A) and OxxxO (approx.0.25 A) distances caused by strong hydrogen bonding are monotonically correlated with OH stretching force constants and frequencies. (4) Excellent quantitative correlation is obtained between calculated and observed infrared gas-phase frequencies. (5) The relative magnitudes of frequencies for symmetric (..nu../sub 1/) and antisymmetric (..nu../sub 3/) stretching modes are found to switch upon passing from H/sub 3/O/sup +/ (..nu../sub 1/<..nu../sub 3/) to H/sub 3/O/sup +/(H/sub 2/O)/sub 3/ (..nu../sub 1/>..nu../sub 3/). (6) The isoelectronic species H/sub 3/O/sup +/(H/sub 2/O)/sub 3/ and OH/sup -/(H/sub 2/O)/sub 3/ are predicted have very similar frequencies for symmetric stretching of hydrogen-bonded OH groups. (7) Addition of a fourth water molecule to the first solvation shell of H/sub 3/O/sup +/ does not lead to any significant stabilization. (8) The most stable isomer of H/sub 13/O/sub 6//sup +/ is found to be an H/sub 9/O/sub 4//sup +/ moiety. (9) The tetrahydrate of the diaquahydrogen ion yields an H/sub 13/O/sub 6//sup +/ structure 2.2 kcal/mole higher in energy.
- Research Organization:
- Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973
- OSTI ID:
- 5426519
- Journal Information:
- J. Chem. Phys.; (United States), Vol. 67:12
- Country of Publication:
- United States
- Language:
- English
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