Neutron scattering and 2H NMR experiments present sensitive tools for the characterization of amorphous ices. Having compared the 2H spin–lattice relaxation behaviour of many different forms of amorphous ice at ambient pressure, they can be attributed to two basic categories, high density and low density states (see Fig. 2.6 and Ref. [82]). As far as the high density states are concerned, there are strong variations in the relaxation parameters and in their transition temperatures to the low density states. This indicates that most of these high density amorphous ices are not relaxed or annealed ones. One of these forms, eHDA appears to be closest to metastable equilibrium which is experimentally manifested by its reproducible T1 relaxation times and its sharp transition temperature to LDA–II. Structure analysis as well as 2H spin–lattice relaxation and 2H lineshape analysis monitor that the sharp transformation of eHDA to LDA–II appears at 123 K in agreement with different techniques [90, 124]. In contrast, the low density amorphous ices exhibit variability in the 2H NMR spin–lattice relaxation times. Beyond all common properties, our second NMR parameter,the Kohlrausch exponent β, shows quite erratic variations from one sample to the other. This indicates that sample preparation and sample history lead to subtle variations of the sample properties. One exception seems to be that in the most relaxed high density form (eHDA), β tends to be larger than in the subsequent low density amorphous ice. A novel finding is that the LDA-II produced in ths way shows a crystallization temperature of about 150 K, whereas the crystallization of HGW already starts at 136 K. LDA-I even crystallizes 14 K lower than LDA-II when heating the system in steps of 2 K every few hours [35]. LDA-II is more stable against crystallization than LDA-I. This enhanced stability of differently produced low density amorphous ices towards crystallization is in agreement with observations by Elsaesser et al. using X-ray diffraction and calorimetric measurements [20]. NMR spin–lattice relaxation and the Debye–Waller factor probe rather fast processes. The temperature dependence of the Debye–Waller factor can identify a very weak sub-Tg anomaly in some of the samples, suggesting possible precursor dynamics below the caloric glass transition onset. While these deviations from harmonic behaviour are slightly visible in the hydrogenated samples (Fig. 6.2), they cannot be corroborated with certainty from the data obtained from deuterated samples. From the results of NMR spin–lattice relaxation, I can draw no conclusions on the question of the existence of glass transition anomalies. The 2H stimulated echo experiments indicate emerging ultraslow, maybe tetrahedral, reorientational motion on a timescale of 5 s · · · 50 s. Since spin–lattice relaxation competes with the stimulated echo correlation decay, relaxation limits applicability of the stimulated echo experiment at lower temperatures (here ≈ 135 K). The upper temperature limit of the experiments is given by crystallization of the samples. Above 135 K the samples gradually crystallize (irreversibly) up to complete crystallization at about 143 K. Nevertheless, in this rather small temperature range, time constants of molecular reorientational dynamics in LDA–II can be extracted. Those time constants show an Arrhenius–like temperature dependence. In terms of glassy materials this would attribute LDA–II to strong glass–formers, i.e. network glasses. Extrapolation of this Arrhenius behaviour to a correlation time of 100 s suggests a caloric glass transition temperature Tg ≈ 126 K which seems to be suitable since the heating rate is much smaller as compared to DSC scans. Even if gradual crystallization is visible within the duration of a stimulated echo experiment, the observed structural relaxation is faster than crystallization towards cubic ice and is in combination with recent findings drom dielectric spectroscopie and penetration experiments a strong hint for a glass transition of LDA–II being the glassy counterpart of liqud water at atmospheric pressure.