Fundamental absorption

These aspects of the optical spectra of solids are illustrated in the upper portion of Figure 1, which displays the reflectance curve (R) at room temperature for a typical semiconductor, GaAs. The fundamental absorption edge around 1.4 eV produces only a weak shoulder. Some structure is apparent in the two features around 3 eV and the large, broad peak near 5 eV. However, the dominant aspect of the line shape is the slowly varyii background. The derivative namre of Modulation Spectroscopy suppresses the uninteresting background effects in favor of sharp, deriva-... 

Fischer R (1972) Absorption and electroabsorption of trigonal selenium near the fundamental absorption edge. Phys Rev B 5 3087-3094... 

Korsunovsky (65-68), Gross weiner (77), Stephens and co-workers (69) and also Markham and Laidler (70) point out that the catalytic activity of semiconductor catalysts in relation to the reaction of oxidation of water under illumination with light from the fundamental absorption band first increases with increasing radiation dose and then attains saturation at sufficiently high doses. 

In this publication, we present the preliminary results of our research effort which is aimed at measuring the magnitude and response time in near the fundamental absorption... 

Si02 (a typical insulator) has a strong absorption rise (called the fundamental absorption edge) in the UV and it is transparent in the visible. 

The absorption spectrum involving the valence band to first empty (conduction) band transitions is usually called the fundamental absorption spectrum. For many crystals, this spectrum lies within the optical range. 

Several III-V semiconductors, such as ALP, GaAs, luSb, AlAs, and InAs, show direct absorption edge transitions. The next example shows the analysis of the fundamental absorption edge for indium arsenide. 

Table 4.3 The frequency dependence expected for the fundamental absorption edge of direct- and indirect-gap materials...

It should be noted that the frequency dependence is different to those expected for direct-gap materials, given by Equations (4.33) and (4.34). This provides a convenient way of determining the direct or indirect nature of a band gap in a particular material by simply analyzing the fundamental absorption edge. Table 4.3 summarizes the frequency dependence expected for the fundamental absorption edge of direct- and indirect-gap materials. 

Figure 4.15 The absorption spectra (near the fundamental absorption edge) of sodium chloride and lithium fluoride at 300 K (reproduced with permission from Palik, 1985).

Recent discussions of stratospheric chemistry have dealt with the effect of freons on ozone balance through a Cl/ClO catalytic destruction of ozone. The fundamental absorption band of CIO is measured to be at 11 /xm. Isotopically substituted CO2 laser based OA absorption measurement technique should allow us to carry out fundamental measurements on CIO and its diurnal variation in the stratosphere to provide yet another important parameter (in addition to NO above) in the stratospheric ozone chemistry. 

X-Ray Absorption Data. The x-ray absorption data shown in Figure 2 were obtained using a computer program based on the mass absorption coefficients, y, total energy, as found in the paper of Storm and Israel (1 ) and using the fundamental absorption equation for x-rays (II). 

A strong resonance Raman fundamental absorption at 1023 cm-1 has been reported for 03 formed by matrix reactions in the Mg-03 system (344). This is in agreement with bands at 1017 and 1010 cm-1 observed for polycrystalline ozonides K03 and Cs03, respectively (132), and at 1038 cm-1... 

The character of interband phototransitions in a semiconductor near the edge of the fundamental absorption band was also studied by means of photoelectrochemical measurements. Assuming, as before, that Lsc, Lp a we obtain for the quantum yield... 

For H4Ru4(CO)i2, a larger number of fundamental absorptions are expected, five Raman-active hydrogen stretching modes (Ai, B1, B2, and 2E) and three ir-active modes (B2 and 2E) coincident with the Raman bands. As mentioned above, the observed spectra consist of only two bands in both the Raman and ir,... 

The absorption edge of (Ga,Mn)As is not sharp, as shown in fig. 20 (Kuroiwa et al. 1998 Szczytko et al. 1999b). This is probably due to impurity band formation caused by the high concentration of ionized Mn and compensating donors (Kuroiwa et al. 1998). Even below the fundamental absorption edge, the absorption coefficient is rather large due to free-carrier (Casey et al. 1975) and intra-Mn absorption. There is no report on the observation of exciton states or photoluminescence, which is probably due to non-radiative recombination, carrier screening, and the formation of an impurity band (Ando et al. 1999). 

Fig. 3.47. Fundamental absorption band of hydrogen top of the compressed gas (at the density of 1014 amagat) center of the liquid (817 amagat) bottom of the solid (972 amagat) after [4],...

In conclusion, we mention that theoretical line shapes were compared with measurements of the hydrogen fundamental absorption for some time. The agreement was generally good see the review articles [422, 342] for examples. Given the impressive consistency that was observed in earlier efforts, one may wonder what the point of the ab initio work is. A brief comparison with the previous efforts seems in order. 

The rototranslational and fundamental absorption spectra of the H2-H complex have been obtained from first principles, for temperatures from 200 to 2500 K [21, 103]. Close-coupled and isotropic interaction approximation calculations give nearly identical values at frequencies from 0 to 6000 cm-1. No laboratory measurements exist for comparison with the calculations. The H2-H system is of considerable interest in stellar environments at such temperatures. 

Q. Ma. Experimental and theoretical study of the collision-induced fundamental absorption spectra of N2-O2 and O2-N2 pairs. J. Quant. Spectroscopy and Rad. Transfer, 69 245, 2001. 

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