Experimental observation of the a relaxation in supercooled water

Intermediate scattering functions for density fluctuation in D2O contained in pores of a Vycor glass have been measured using an improved neutron spin -echo spectrometer at two supercooled temperatures. The measurements cover the time range from 1 to 2300 ps with the Q range spanning the first diffra ction peak of water. The time correlation functions can be fitted to a stre tched exponential relaxation function with a e-dependent amplitude. Both th e stretch exponent and the relaxation time peak approximately at the Q valu e corresponding to the first diffraction peak, confirming the validity of t he mode couplings idea in supercooled water.