Quasielectron electron scattering from gaseous H 2 , D 2 , a 50:50 mixture of H 2 and D 2 , and HD is investigated with 2.25 keV impact energy and a momentum transfer @q of 19.7 a.u. The energy transfer is less than the dissociation energy. The spectral positions of the H and D recoil peaks agree with Rutherford scattering theory. Surprisingly, in the spectrum of the 50:50 H 2 -D 2 mixture, the integrated intensity of the H peak is 31% 4% lower (as compared to that of D) than predicted by

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... ford scattering, despite equal screening of nuclear charges by the electrons. In contrast, the ratio of scattering intensities from H and D in HD agrees with the predictions of Rutherford scattering. Comparison is made with neutron Compton scattering results from the same systems, but at higher energy transfers causing bond breaking. Possible theoretical explanations are outlined.