Electron-atom Compton profiles due to the intramolecular motions of the H and D atoms in HD

We report an atomic momentum spectroscopy (AMS) experiment on HD, performed at a scattering angle of 135 degrees and at an incident electron energy of 2.0 keV. The electron-atom Compton profiles due to the intramolecular motions of the H and D atoms in HD were obtained. The two Compton profiles are shown to be identical with each other in both shape and intensity, proving that the experimental responses of the intramolecular atomic motions are disentangled from the effect of molecular translational motion. It is also shown that the Compton profiles are in agreement with associated quantum chemistry-based calculations, indicating that the large momentum transfer limit is achieved under the experimental conditions. These observations demonstrate the ability of AMS not only to map the intramolecular motion of each atom with different masses but also to perform elemental composition analysis of a molecular system.