Observation of fractional Stokes-Einstein behavior in the simplest hydrogen-bonded liquid.
Quasielastic neutron scattering has been used to investigate the single-particle dynamics of hydrogen fluoride across its entire liquid range at ambient pressure. For T>230 K, translational diffusion obeys the celebrated Stokes-Einstein relation, in agreement with nuclear magnetic resonance studies. At lower temperatures, we find significant deviations from the above behavior in the form of a power law with exponent xi=-0.71+/-0.05. More striking than the above is a complete breakdown of the Debye-Stokes-Einstein relation for rotational diffusion. Our findings provide the first experimental verification of fractional Stokes-Einstein behavior in a hydrogen-bonded liquid, in agreement with recent computer simulations [S. R. Becker, Phys. Rev. Lett. 97, 055901 (2006)10.1103/PhysRevLett.97.055901].
Fernandez-Alonso
F
F
ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11 0QX, United Kingdom. F.Fernandez-Alonso@rl.ac.uk
Bermejo
F J
FJ
McLain
S E
SE
Turner
J F C
JF
Molaison
J J
JJ
Herwig
K W
KW
D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004058:Diffusion; D004735:Energy Transfer; D006860:Hydrogen Bonding; D021241:Spectrometry, Mass, Electrospray Ionization; D013696:Temperature