Deuterium isotope effects on the dipole moment and polarizability of hydrogen chloride and ammonia

Abstract

A previously described adaptation of the conventional Debye procedure for the direct determination of small dipole moment and polarizability differences between two polar gases is applied to the isotopic pairs DCl-HCl and ND/sub 3/-NH/sub 3/. The dipole moment difference obtained for the first isotopic pair, by using the Debye-Van Vleck equation for electric susceptibility, ..mu..(DCl) - ..mu..(HCl) = 0.005/sub 5/ +/- 0.0002 D, is consistent with published spectroscopically determined values of ..mu../sub 00/(DCl) and ..mu../sub 00/(HCl), while that obtained by using the classical Debye equation is not. For the second pair, use of the Debye-Van Vleck equation, along with a correction for thermal population of vibrationally excited levels, is shown to be essential and yields ..mu..(ND)/sub 3/ - ..mu..(NH/sub 3/) = +0.013/sub 5/ +/- 0.001 D and ..cap alpha..(ND/sub 3/) - ..cap alpha..(NH/sub 3/) = -(2.2 +/- 1.7) x 10/sup -26/ cm/sup 3/.