Numerous treatments of the diffuse r efl ecting properties of scattering media have been d escribed. Many theories give an adequate account of the refl ectance for a specific set of conditions for which the model was constructed and the soluti on t ested experimentally. Only those models which are considered to be fairl y general are considered her e.It is conveni ent to di vide the theories into those based upon continuum models and those based upon s tatistical models. The continuum m odels typica ll y describe the scatterin g a nd absorbin g properties of a given m edium in t erm s of two phenomenological constants. These models may all be regarded as varying levels of approxima t e soluti on to the general equation of radi ative tra nsfer. This provides a convenient basis for compariso n of the various theories.The statistical models a re based upon a summa tion of transmittances a nd r efl ectances fr om individual l ayers or parti cles. Thus, ~o m e ass um ptions must be m ade abo ut the n ature of the fund amenta l units, and the validity of the ultim a te result will depend upon how closely these assumptions correspond with r eality. Only the statistical models lead to ex pressions fr om which absolute absorptivities and sca ttering coefficients can be calculat ed and r elated to the actual particle characteristics.The relationship between the various models will be discussed and the features which typify the ab~o rptivity and scatterin g coeffici ent according to each will be compared and related to the available experimental data. This leads t o a consideration of the charac teristics of appropriate model systems and standards.Key words: Absolute absorptivities; continuum models; diffuse reflectance; r adiative transfer; reflectance spectra; scatt ering coefficients ; statistical models. List of Principal Symbols UsedH-integral of Chandrasekhar (equation (35) ) (Note: Where a given letter is used in both capital and lower case form (e.g., r,R and t,T), the capital letter refers to the macroscopic observable and the lower case letter to the corresponding variable for an individual particle or layer of the material. A bar over a given symbol means the average value for that variable). (5)) scattering function (equation (2)) source func tion (eq ua tion (4)) absorptivity Kubelka-Munk absorption constant (equations (16) and (17) H(iJ.)

The EPR and optical spectra of vanadium in the Na2O–B2O3 glass system have been analyzed. It is found that the data can best be interpreted in terms of a vanadyl-type structure in a ligand field of fourfold symmetry. Good correlation of the optical and EPR data is achieved through molecular orbital calculations, which provide a qualitative description of the behavior of the coordination sphere as the Na2O content of the glass is varied. The model proposed is one in which there is a dilation of the ligand shell corresponding to the boric oxide anomaly superposed on an over-all tendency of the ligand—metal distance to decrease as [Na2O] increases. The hyperfine coupling terms as well as the g tensor and optical data support this model.

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Articles you may be interested inOxygen17 NMR and EPR studies of water exchange from the first coordination sphere of gadolinium(III) aquoion and gadolinium(III) propylenediaminetetraacetate J. Chem. Phys. 73, 5909 (1980); 10.1063/1.440148 NMR proton relaxation in compressed supercritical water

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