Anomalous quasi-elastic electron scattering from single H2,D2 and HD molecules at large momentum transfer - Indications of nuclear spin effects

Quasi-elastic electron scattering from gaseous H2, D2, a 50:50 mixture of H2 and D2 and HD is investigated with 2.25 keV impact energy and 100o scattering angle, corresponding to a momentum transfer ℎq of 19.7 a.u. The energy transfer is less than the H-H, H-D or D-D bond dissociation energy. The spectral positions of the H and D recoil peaks are adequately explained by Rutherford scattering theory. Surprisingly, in the spectrum of the 50:50 H2-D2 mixture, the integrated intensity of the H peak is 31±4 % lower (as compared to that of D) than predicted by Rutherford scattering, despite equal screening of nuclear charges by the electrons in all molecules. In contrast, the ratio of scattering intensities from HD agrees with the predictions of Rutherford scattering. Comparison is made with previous neutron Compton scattering (NCS) experiments from the equimolar H2-D2 mixture and HD, at much higher energy transfer in the range which can cause H-H bond breaking. The NCS results showed the same deviation (about 30%) from theory in both the H2-D2 mixture and HD. Connection to existing theories (on scattering dynamics of entangled particles) is made