Showing papers in "Transactions of The Faraday Society in 1957"

The difference in the intermolecular forces of H2O and D2O

Abstract: The lattice energy of a compound at O deg K can be obtained from the heat of sublimation at O deg K, the zero-point energies due to the various intermolecular vibrations, and the difference between the crystal and the gas in the intramolecular zero-point energies. The difference in the lattice energies of isotopic molecules which have the same crystal structure is a good measure of the difference in their intermolecular forces. The lattice energy of H/sub 2/O and the difference in lattice energies of H/sub 2/O and D/sub 2/O have been calculated from calorimetric and spectroscopic data. The lattice energy of D/sub 2/O at 0 deg K is higher than that of H/sib 2/O by 1.27 plus or minus 0.6 kJ mole/sup -1/. The difference is presumably due to the different intermolecular forces consequent on the anharmonic zero-point intramolecular vibrations, and the difference of dipole moments is probably the major contribution. This is the first clear evidence that isotopic molecules may have appreciably different intermolecular forces. Tbe lattice energy of ice at 0 deg K is higher than is usually assumed because of the difference of zero-point energies between the solid and the vapor and it amounts to 56.0 xmore » 0.7 kJ mole/sup -1/. Most of the assigned error is caused by the uncertainties in the distribution of intermolecular rotational frequencies. (auth)« less