Modeling, metal absorption

Some researchers have doubted whether nonporphyrin metal compounds exist at all in petroleum (Goulon et al., 1984 Berthe et al., 1984). This speculation is based on the similarities in spectral features of petroleum-bound metals and model-metal porphyrin compounds from selected petroleums under the examination of x-ray absorption, photoelectron, and laser desorption spectroscopies. Interpretation of spectra from these methods, however, is uncertain and difficult given the lack of sufficient data on model compounds, particularly nonporphyrin metals and in a petroleum environment or matrix. 

Part 1, Theory and Computational Methods, opens with a chapter by M. A. Yurkin (Russia) who describes in detail the Discrete Dipole Approximation (DDA) approach, which is an efficient method to study the absorption and scattering of metal nanoparticles of arbitrary shapes. This chapter will serve as an important reference for theoreticians to model metal nanoparticles. Chapter 3 reports DDA results for nanoparticles of different sizes and shapes. This systematic analysis, inspired by recent literature, should represent an important reference for both experimentalists and theoreticians to verify and compare the absorption and scattering spectra of different nanoparticles. While these first two chapters are completely dedicated to metal nanoparticles. Chapter 4 introduces the discussion about the molecular counterpart. In this chapter E. Fabiano (Italy) sheds light on the optical and photophysical... 

For opaque materials, the reflectance p is the complement of the absorptance. The directional distribution of the reflected radiation depends on the material, its degree of roughness or grain size, and, if a metal, its state of oxidation. Polished surfaces of homogeneous materials reflect speciilarly. In contrast, the intensity of the radiation reflected from a perfectly diffuse, or Lambert, surface is independent of direction. The directional distribution of reflectance of many oxidized metals, refractoiy materials, and natural products approximates that of a perfectly diffuse reflector. A better model, adequate for many calculational purposes, is achieved by assuming that the total reflectance p is the sum of diffuse and specular components p i and p. ... 

In this work, atmospheric particles (PM 10 and PM 2.5) were collected by a dichotomos air sampler. Several leaching procedures were investigated for decomposition of heavy metals. The digests were pre-concentrated with sodium diethyldithiocarbamate. The determinations were canted out on a Vartan Model AA-220 atomic absorption spectrometer. The instrarment was equipped with a GTA-110 graphite furnace system. Table 1 shows the concentrations of heavy metals associated with PM 10 and PM 2.5 particles. Table 1. Concentrations of heavy metals in PM 10 and PM 2.5 atmospheric particles (ng/m )... 

The interpretation of these remarkable properties has excited considerable interest whilst there is still some uncertainty as to detail, it is now generally agreed that in dilute solution the alkali metals ionize to give a cation M+ and a quasi-free electron which is distributed over a cavity in the solvent of radius 300-340 pm formed by displacement of 2-3 NH3 molecules. This species has a broad absorption band extending into the infrared with a maximum at 1500nm and it is the short wavelength tail of this band which gives rise to the deep-blue colour of the solutions. The cavity model also interprets the fact that dissolution occurs with considerable expansion of volume so that the solutions have densities that are appreciably lower than that of liquid ammonia itself. The variation of properties with concentration can best be explained in terms of three equilibria between five solute species M, M2, M+, M and e ... 

Parker [55] studied the IN properties of MEH-PPV sandwiched between various low-and high work-function materials. He proposed a model for such photodiodes, where the charge carriers are transported in a rigid band model. Electrons and holes can tunnel into or leave the polymer when the applied field tilts the polymer bands so that the tunnel barriers can be overcome. It must be noted that a rigid band model is only appropriate for very low intrinsic carrier concentrations in MEH-PPV. Capacitance-voltage measurements for these devices indicated an upper limit for the dark carrier concentration of 1014 cm"3. Further measurements of the built in fields of MEH-PPV sandwiched between metal electrodes are in agreement with the results found by Parker. Electro absorption measurements [56, 57] showed that various metals did not introduce interface states in the single-particle gap of the polymer that pins the Schottky contact. Of course this does not imply that the metal and the polymer do not interact [58, 59] but these interactions do not pin the Schottky barrier. 

In an earlier work, we have proposed a theoretical procedure for the spectroscopy of antiferromagnetically (AF) coupled transition-metal dimers and have successfully applied this approach to the electronic absorption spectrum of model 2-Fe ferredoxin. In this work we apply this same procedure to the [Fe2in - 82) P o - CeH48)2)2 complex in order to better understand the electronic structure of this compound. As in our previous work" we base our analysis on the Intermediate Neglect of the Differential Overlap model parameterized for spectroscopy (INDO/S), utilizing a procedure outlined in detail in Reference 4. 

---