Evidence of the presence of optic-like collective modes in a liquid
03 Dec 2008



The dynamics within hydrogen bonded liquids are key to understanding the fundamental interactions which give rise to the cohesion energy being governed by strongly directional electrostatic forces.

The energy and wave vector dependence (Q) of collective optic-like modes in liquid DF.

Hydrogen bonded systems significantly differ from ionically bonded solids in the sense that the heavy atoms bridged by the hydrogen bonds approach each other more closely than expected given their ionic radii. Also, these systems are known to exhibit strong cooperative behaviour such as the appearance of small clusters in the gas phase.

Inelastic neutron scattering data taken on MARI from liquid deuterium fluoride (DF) close to the melting point show, in addition to quasielastic and heavily damped acoustic motions, an intense band centered at about 27meV along with a broader higher energy feature. Observation of the former band provides the first direct verification of the existence within the liquid state of collective optic-like excitations as predicted by molecular dynamics simulations. The latter corresponds to mainly reorientational motions also predicted by simulation.

FJ Bermejo (University of the Basque Country, Spain), JW Taylor, SE McLain (ISIS), I Bustinduy (University of the Basque Country, Spain), JFC Turner (University of Tennessee, USA), MD Ruiz-Martin (ILL, France), C Cabrillo, R Fernandez-Perea (Consejo Superior de Investigaciones Científicas, Serrano, Spain).

Research date: December 2006

Further Information

Prof FJ Bermejo, [javier@langran.iem.csic.es] FJ Bermejo et al., Phys. Rev. Lett. 96 (2006) 235501​