COMMENTS ON H D ISOTOPE EFFECTS ON POLARIZABILITIES OF SMALL MOLECULES - CORRELATION WITH VIRIAL-COEFFICIENT, MOLAR VOLUME, AND ELECTRONIC 2ND MOMENT ISOTOPE EFFECTS/

Literature data on H/D isotope effects on polarizability are reviewed, An argument based on perturbation theory correlates the isotopic diff erences with electronic transition moments via vibrational averaging. The contribution of the second moment isotope effect is especially imp ortant. The approach is first illustrated with a calculation on H-2/D2 and then employed to correlate differential refractive index data on about twenty other H/D isotopic pairs. A table of bond polarizability isotope effects is presented which permits the estimation of polarizab ility isotope effects for various kinds of H/D substituted compounds. Coupling these results with known isotope effects on vibrational ampli tude permits calculation of vapor phase virial coefficient isotope eff ects, while combination with refractive index data on liquids yields r easonable values for the sum of the isotope effects on molar volume an d electronic second moment. However the quantitative correlation of th e polarizability isotope effect with isotope effects on vapor pressure or thermodynamic activity is less direct.