Anharmonicity as a reaction indicator: thermal vibrations in the graphitic carbon nitride precursor melamine

In our proposed study, we investigate melamine (C3N6H6) as a precursor for the graphitic carbon nitride (g-CN) materials with interesting properties for e.g. catalysis. A previous electron density study of melamine by synchrotron single crystal X-ray diffraction (SCXRD) at 25 K, lead to a proposed mechanism for the condensation reaction of melamine through melam to g-CN by evaporation of ammonia. The condensation hypothesis is based on structural asymmetry, one amine group in melamine is significantly more pyramidal (like ammonia) than the two other, and thus strongly relies on accurate hydrogen atom positions. Single crystal neutron diffraction experiments could uniquely offer information on especially unambiguous hydrogen positions, anisotropic atomic displacement parameters and possibly anharmonic vibrations, which could validate the conclusions from the SCXRD study. We, furthermore, intend to investigate anharmonic motion as a reaction indicator for the condensation process. This requires accurate determination of structure and anharmonic vibrational parameters of nitrogen and hydrogen at several temperatures, which only neutron diffraction can provide. We apply for 7 days of beamtime at the SXD instrument, allowing us to conduct neutron diffraction experiments at 25, 100, 300 and 400 K.