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The formation of an ether adduct was studied by analyzing the thermolysis of (NH4)HCO37 and proton-irradiated CO2/H2O ice mixtures. Carbonic acid, H2CO3, is an essential compound in biological and geochemical carbonate-containing systems. A cryogenic method for its isolation was developed. The solutions of two reactants KHCO3 or Cs2CO3 and HCl were introduced on a cryoplate cooled to 78 kelvin. Methanol was chosen as one of the first solvents as it can be easily quenched into the glassy state.

Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction have shown that the two crystal polymorphs [alpha]-[H.sub.2]C[O.sub.3] and [beta]-[H.sub.2]C[O.sub.3] are formed from two different amorphous states, indicating polyamorphism for [H.sub.2]C[O.sub.3]. The studies have shown that the two amorphous states of [H.sub.2]C[O.sub.3] are connected by a first order-like phase transition.

Crystallization kinetics of hyperquenched D2O liquid has been studied by Fourier transform infrared spectroscopy by determining the irreversible change in the spectra of stretching vibrations of the decoupled OH oscillator in ≊12 mol % HOD in D2O. The kinetics follows an almost exponential behavior with time. The exponent to the crystallization time, n, increases from its value of 1.0 at 152 K to 1.2 at 147 K and its value is slightly lower than that of H2O. The combined results of H2O and D2O indicate that temperature rather than the mass of the molecules determines n. Interpretation of n in terms of the morphology of grains formed seems inconsistent in view of the observed temperature effect. It is suggested that an alternative interpretation of n in terms of distribution of diffusion times, or time independent activation energy (barrier height to crystallization), is more appropriate. Calorimetric measurements for the crystallization of H2O yield results consistent with those from infrared spectroscopic study. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Metastable liquid water, obtained by heating its hyperquenched glassy state above its glass→liquid transition temperature, crystallizes to cubic ice. Kinetics of this crystallization has been studied by Fourier transform infrared spectroscopy by determining the change in the spectra of stretching vibrations of the decoupled OD oscillator in 3.6 mole % HOD in H2O. The crystallization kinetics follows the equation x=[1-exp(-ktn)] and is diffusion controlled. Annealing at a temperature below its glass→liquid transition temperature alters this kinetics as the grain–growth process begins to control the early stages of crystallization. [ABSTRACT FROM AUTHOR]