Temperature Dependences of Nuclear-Transfer and Spin-Relaxation Phenomena of Water Adsorbed on Silica Gel

Abstract

NMR relaxation‐time measurements have been made from 193° to 374°K on the protons in a sample of ¾ statistical monolayer of water adsorbed on silicagel.Protons in two different environmental states were observed. Proton transfers occur between these two environmental states. For the first time, the T 2 value for the longer T 2 state has been observed without shortening by nuclear transfers. This longer T 2 value increases with temperature in accordance with an activation energy of approximately 7 kcal/mole. The weighted average T 1 value has a similar temperature dependence in the range 225° to 270°K. The data were analyzed in detail by use of previously developed theory. Near room temperature, the activation energy for proton transfer is 4.9 kcal/mole, and the average lifetime of a proton in a given state is a few milliseconds. The protons in both states experience very rapid motion; one of the states has an additional slow motion.