X-ray diffraction data show that there are at least two forms of amorphous solid water which differ in density and second nearest-neighbor oxygen–oxygen distribution. (a) The lower density form, made at 77 °K, has a diffraction pattern consistent with a structure that has oxygen–oxygen nearest-neighbor tetrahedral symmetry on average, and a nearest neighbor O–O separation of 2.76 Å with small dispersion. The density of this material is estimated to be 0.94 g cm−3. While it is not possible to uniquely define the structure, the data available support the notion that its fundamental characteristic is the existence of a randomized network of hydrogen bonds with O–O–O angular distribution derived from (i.e., centered about) that of ice Ih. Comparison of neutron diffraction and x-ray diffraction data suggests strongly that the first shell hydrogen bonds are nearly linear and that orientational correlations between water molecules are limited to nearest neighbors. (b) The higher density form, made at 10 °K, has a diffraction pattern similar to, yet distinctively different from, that of the high temperature deposit. The O–O nearest neighbor distance is the same, 2.76 Å, but the dispersion in this separation is larger in the low temperature form. The diffraction pattern shows an extra peak at 3.3 Å, corresponding to about 1.4 molecules, the existence of which is responsible for the estimated higher density, namely 1.1 g cm−3. The data are consistent with several models which share the feature of introducing small O–O–O angles into the structure. We discuss the relationships between our data, and inferences from the data, and the corresponding data for liquid water.

Water vapor that condenses on a metal surface at 10 degrees K forms a noncrystalline phase of estimated density 1.2 grams per cubic centimeter. X-ray diffraction data of high precision and resolution have been analyzed to yield oxygen atom pair correlation functions. The positional correlation in amorphous solid water extends over only a few molecular radii, and the radial distribution of nearneighbor oxygen atoms in amorphous solid water is qualitatively different from that found in the low-pressure ice modifications. Amorphous solid water is a useful material for liquid water models because it can be studied under conditions such that the effects of static disorder and thermal excitation can be separated.

Raman spectra of amorphous solid H 2 0. [H 2 0(as)J. D20(as). and 12% H 2 0 in D 2 0(as) were measured over a temperature range from 30 to 120'K. The spectra of H20(as) resemble those of liquid water more than they do those of ice Ic or ice Ih. The spectra suggest that the water molecules are located in two or three types of distinguishable environments depending on the details of the assignment. No structural changes were observed between 30 and 120'K. but at -160'K the amorphous samples transformed rapidly and irreversibly to ice le.

The output and transmission characteristics of both single and double (tandem) integrating spheres have been studied with a lead-salt diode laser in the 2000-cm(-1) spectral region. For an f/20 input beam, the effective length is about eight times the diameter of the sphere. The corresponding transmittance is ~10(-5) for the tandem spheres. The output beam has a Gaussian profile.

The absolute quantum yield for the dissociation of glyoxal into carbon monoxide following excitation to seven (00, 71, 51, 81, 81 72, 21, 81 41) single vibronic levels (SVL) in the 1Au state are presented. Samples in the 1–10 torr pressure regime were studied. Significant vibronic and pressure dependencies were observed for all seven SVL examined. Dependencies arising solely from the characteristics of specific vibronic modes were found following excitation to two levels (81 and 81 41). The results are interpreted in terms of an excited-state mechanism which includes dissociation from vibrationally excited 3Au levels.