LIQUID WATER IN THE DOMAIN OF CUBIC CRYSTALLINE ICE I-C

Vapor-deposited amorphous water ice, when warmed above the glass trans ition temperature (120-140 K), is a viscous liquid which exhibits a vi scosity vs temperature relationship different from that of liquid wate r at room temperature. New studies of thin water ice films now demonst rate that viscous liquid water persists in the temperature range 140-2 10 K, where it coexists with cubic crystalline ice. The liquid charact er of amorphous water above the glass transition is demonstrated by (1 ) changes in the morphology of water ice films on a nonwetting surface observed in transmission electron microscopy (TEM) at around 175 K du ring slow warming, (2) changes in the binding energy of water molecule s measured in temperature programmed desorption (TPD) studies, and (3) changes in the shape of the 3.07 mu m absorption band observed in,ora ting angle reflection-absorption infrared spectroscopy (RAIRS) during annealing at high temperature, whereby the decreased roughness of the water surface is thought to cause changes in the selectin rules for th e excitation of O-H stretch vibrations, Because it is present over suc h a wide range of temperatures, we propose that this form of liquid wa ter is a common material in nature, where it is expected to exist in t he subsurface layers of comets and on the surfaces of some planets and satellites, (C) 1997 American Institute of Physics.