This can be revealed from the momentum distribution n(p), which is a very sensitive probe of the potential of mean force experienced by the protons in hydrogen-bonded systems. We have explored the details of n(p) in ice at T=271 K using a combination of deep inelastic neutron scattering and path-integral Car-Parrinello molecular dynamics simulations. The neutron data have been interpreted within the framework of the impulse approximation, which allows us to extract the three-dimensional n(p). Experimental and simulation data have been successfully interpreted with an anisotropic Gaussian model in which the proton essentially moves in a harmonic well along each direction, but with a marked anisotropy between motions parallel and perpendicular to the bond-stretching direction.
The proton momentum distribution in ice parallel (p||) and perpendicular (p ) to the bond-stretching direction.
D Flammini, A Pietropaolo, R Senesi, C Andreani (Università di Roma Tor Vergata, Italy), F McBride, A Hodgson (Liverpool University), L Lin, R Car (Princeton University USA), MA Adams (ISIS)
Research date: May 2010
Contact: Prof C Andreani, firstname.lastname@example.org
Further reading: C Andreani et al., Adv Phys 54 (2005) 377