The local structure of triphenyl phosphite studied using spallation neutron and high-energy X-ray diffraction

Spallation neutron and high-energy X-ray diffraction experiments have been performed to investigate the local structural changes in triphenyl phosphite (TPP) in the crystalline, glacial, glassy, and supercooled liquid phases. The hydrogen/deuterium first-order difference method shows a large increase in intensity due to additional hydrogen correlations in the crystalline spectra compared to the glass and supercooled liquid at ∼3.0 and 3.4 Å. These features are shown to be largely due to inter-phenyl ring H-C/H interactions, which are probably associated in part with the formation of weak intermolecular hydrogen bonds. The high-energy X-ray diffraction data show a decrease in correlations at 3.12 Å which is attributed to changes in C-O/P intramolecular interactions between the glacial and crystalline forms. The structural evolution of the glacial state was also measured over time using total neutron diffraction. The largest structural differences between the early glacial and crystalline states are observed at 3.0 and 4.5 Å. Moreover, as the transformation progresses, the glacial spectra cannot be adequately described as a simple mixture of supercooled liquid and crystalline components. These results suggest that changes in molecular conformation and nearest-neighbor interactions are responsible for the existence of the glacial state.