Proton quantum coherence observed in water confined in silica nanopores

Abstract

Deep inelastic neutron scattering measurements of water confined in nanoporous xerogel powders, with average pore diameters of 24 and 82 Å, have been carried out for pore fillings ranging from 76% to nearly full coverage. DINS measurements provide direct information on the momentum distribution n͑p͒ of protons, probing the local structure of the molecular system. The observed scattering is interpreted within the framework of the impulse approximation and the longitudinal momentum distribution determined using a model independent approach. The results show that the proton momentum distribution is highly non-Gaussian. A bimodal distribution appears in the 24 Å pore, indicating coherent motion of the proton over distances d of approximately 0.3 Å. The proton mean kinetic energy ͗E K ͘ W of the confined water molecule is determined from the second moment of n͑p͒. The ͗E K ͘ W values, higher than in bulk water, are ascribed to changes of the proton dynamics induced by the interaction between interfacial water and the confining surface.

Quantum effects in water: proton kinetic energy maxima in stable and supercooled liquid

“…Dashed line marks the position of the triple point. The error bars are derived from the least squares fitting procedure parameter errors [7,10,11] Similar remarkable features are found in the n(p). A plot in Figure 3 of the radial momentum distributions 4πp 2 n(p) most effectively highlights the differences between the n(p)'s measured in the different states.…”

“…The error bars are less than 1% and were derived from the least squares fitting procedure parameter errors [7,10,11]. The additional intensities in the wings of the data at T = 271.00 K (black) and T = 269.00 K (purple), must be due to the protons being more localised in the supercooled phase.…”

“…values are derived from the least squares fitting procedure parameter errors [7,10,11]. Temperature uncertainties is 0.01 K in all measurements.…”

“…Dashed line marks the temperature of the triple point. The error bars are derived from the least squares fitting procedure parameter errors [7,10,11].…”

Anomalous Ground State of the Electrons in Nanoconfined Water

“…The proton momentum distribution for the two Nafion samples compared to that of water is shown in Ref 4. The oscillations are indicative of the proton being coherently distributed in a double well with a separation of the wells on the order of 0.3Å 17 , as determined by the position of the minimum. 6 The kinetic energy has gone up because each of these wells is more tightly binding the proton than the covalent bond of the isolated water molecule.…”