Proton tunnelling in intramolecular hydrogen bonds: a neutron study

Zero-point vibrational energy (ZPE) and nuclear quantum tunnelling (NQT) are nuclear quantum effects (NQEs) that can be measured directly only using neutron Compton scattering (NCS). This proposal’s ambition is to extend the applicability of the NCS technique on VESUVIO into the realm of the local proton quantum dynamics in the intramolecular hydrogen bonds by investigating two benchmark systems for studying hydrogen tunnelling, malonaldehyde (MA) and tropolone (TR), in both hydrogenated and OD-deuterated forms. The ground-state tunnelling splitting in both MA and TR was investigated both experimentally and theoretically, and the main result was that the tunnelling would be partially quenched when the transferring hydrogen is substituted by deuterium. However, in the most recent theoretical study of proton tunnelling in the MA, Roberto Car et al. authors proposed that the correlations of the molecular motions are sufficient to smooth non-Gaussian NMDs associated with deep tunnelling in the one-dimensional double-well model. However, in the TR, this smoothing mechanism may not exist. The proposal aims at checking this hypothesis.