The pressure dependence of the HOMO-LUMO transition energy and the frequency of the longest wavelength longitudinal optical vibration of 45 Å diameter CdSe clusters in methanol-ethanol solution have been measured up to 50 kbar. The LO mode shifts to higher frequency at a rate of 0.43 cm -1/kbar, which corresponds to a Grüneisen parameter of 1.1. The HOMO-LUMO transition shifts to higher energy at 4.5 meV/kbar, yielding a deformation potential of 2.3 eV. The pressure dependence of these properties closely resemble those of the corresponding bulk solid, confirming the point of view that the lattice properties of these clusters resemble those of the bulk, even though the optical properties are quite distinct. © 1988 American Institute of Physics.

The resonance Raman spectrum of 45( + - 3) Å diameter CdSe clusters was measured. The incident photons were resonant with the HOMO-LUMO transition in the clusters. At low temperature, one mode at 205 cm-1 is observed, as well as two overtones, with the integrated areas under these peaks in the ratio of 9:3:1. This mode is assigned as the longest wavelength longitudinal optical vibration of the cluster. The strength of the coupling between the lowest electronic excited state and the LO vibration is found to be 20 times weaker in these clusters than in the bulk solid. The CdSe cluster resonance Raman spectrum is shown to be consistent with the recently measured homogeneous cluster absorption spectrum. © 1989 American Institute of Physics.

Stereoradiographs have been used on occasion for three-dimensional reconstruction and measurement of objects in radiology and radiotherapy. The lack of a good stereoradiographic technique has limited the uses of steroradiographic exposures. In this paper, the principle of the double-image is outlined and a method of applying this principle to stereoradiographic exposures is developed. A computer program has been developed from geometrical considerations to analyze the stereobronchogram and to calculate the dimensions of the objects in question. The applications of this technique are discussed and its use in evaluating lung casts is described.

We describe a synthesis of nanometer-sized clusters of CdSe using organometallic reagents in inverse micellar solution and chemical modification of the surface of these cluster compounds. In particular we show how the clusters grow in the presence of added reagents and how the surface may be terminated and passivated by the addition of organoselenides. Passivation of the surface allows for the removal of the cluster molecules from the reaction medium and the isolation of organometallic molecules which are zinc blende CdSe clusters terminated by covalently attached organic ligands. Preliminary cluster characterization via resonance Raman, infrared, and NMR spectroscopy, X-ray diffraction, transmission electron microscopy, and size-exclusion chromatography is reported. © 1988, American Chemical Society. All rights reserved.