Defect structure and molecular dynamics of doped ice and natural snow

Abstract

Ice doped with from 1 to 1000 ppm HCl, HBr, HI, NaCl or NaNO3 has been studied with 1H-NMR methods. The spectrum consists in general of a small narrow peak superposed on a broader peak. The linewidth and the spin-lattice relaxation time of the broad peak (from the solid part of the ice samples) have been determined as a function of temperature from about -9O°C to the melting point. The temperature dependence indicates that the dopants create defects in ice different from the intrinsic defects in pure hexagonal ice as the observed activation energies, from 20 to 30 kJ mol-1, are significantly smaller than the activation energy observed for pure ice (ca. 60 kJ mol-1). We have not succeeded in observing a liquid phase in pure ice, and therefore conclude that any liquid phase reported in 'pure' ice must be due to impurities. Also, samples of natural snow have been studied. The experimental results show that the bulk of the snow gets purer as the snow anneals on the ground. © Acta Chemica Scandinavica 1997.