Fundamental absorption band

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. 

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. 

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... 

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],...

The infrared spectrum therefore consists of a number of absorption bands arising from infrared active fundamental vibrations however, even a cursory inspection of an i.r. spectrum reveals a greater number of absorptions than can be accounted for on this basis. This is because of the presence of combination bands, overtone bands and difference bands. The first arises when absorption by a molecule results in the excitation of two vibrations simultaneously, say vl5 and v2, and the combination band appears at a frequency of -I- v2 an overtone band corresponds to a multiple (2v, 3v, etc.) of the frequency of a particular absorption band. A difference band arises when absorption of radiation converts a first excited state into a second excited state. These bands are frequently of lower intensity than the fundamental absorption bands but their presence, particularly the overtone bands, can be of diagnostic value for confirming the presence of a particular bonding system. 

Thermal emission is based on measuring the fundamental absorption bands of glucose at 10pm, using the body s naturally emitted infrared radiation as the source. The detection equipment is similar to that used for infrared absorption spectroscopy. Malchoff et al.82 reported the evaluation of a prototype that measures the infrared emission from the tympanic membrane. 

The absorption of light close to the fundamental absorption-band edge of an oxide leads to the excitation of an electron in the oxide ion followed by a charge-transfer process to create an exciton (an electron-hole pair) which is essentially free to migrate through the lattice,... 

The existence of photodesorption may be understood in the following way. Photoconductivity studies 104) show that irradiation within the fundamental absorption band of zinc oxide leads to the production of electrons and holes. Other things being equal, these are free to participate in adsorption and desorption, and will react with oxygen as follows ... 

A prominent method associated with PAT, not only in drying, but also in association with blend uniformity and wet granulation, is near NIR. Fundamental absorption bands occur in the mid-IR region but these absorbances require dilution to bring them... 

At room temperature, the molecules are still in the non-excited state y = 0, that is, (vib)o = l 2hv (energy at OK). Besides the standard transition Ay = +1, that corresponding to Ay = +2 and forbidden by this theory, appears weakly when the fundamental absorption band is particularly strong (for example, in the case of elongation vibrations in organic compounds containing a carbonyl bond C=0 (e.g. ketones or aldehydes). 

The spectra observed in this region involve mainly hydrogen stretching vibrations in, for example, C—H, N—H, and O—H bonds. A fundamental absorption band at a given frequency may be accompanied by bands at all multiples of this frequency. These additional bands are called overtones. The first overtone is much weaker than the fundamental, and successive overtones are progressively weaker still. Absorption bands may also occur at a frequency which is the sum or difference of two fundamental frequencies, or the sum or difference of an overtone and a fundamental frequency. These are called combination frequencies. Overtone and combination bands are most readily observed on comparatively thick samples in the region between the visible and 2.5 pi, where there are no fundamental absorption bands, and all the bands arise from this cause. 

The fundamental absorption band of PH in its ground state X was observed at high resolution using a tunable diode laser spectrometer eighteen lines betwen 2224.4125 and 2107.8160 cm" (4.50 to 4.74 pm) have been identified as P-branch transitions with N" = 3 to 7 and 9, where each transition exhibits the fine-structure triplet splitting due to AJ = AN transitions between the three sublevels (J = N +1, N, N -1) of the respective rotational levels N" and N. Two further lines at 2292.1918 and 2308.1542 cm" (-4.3 pm) have been identified as the R-branch transitions with N", J " = 0,1 and 1,0. Hyperfine splitting could not be resolved. The analysis, which included rotational and centrifugal distortion effects as well as spin-spin... 

Other factors bring about even more absorption peaks. Overtones (harmonics) of fundamental absorption bands may be seen in IR spectra even though these overtones occur with greatly reduced intensity. Bands called combination bands and difference bands also appear in IR spectra. 

Absorption Edge of Amorphous Ge and Si FUNDAMENTAL ABSORPTION BAND INDEX OF REFRACTION, SUM RULES EFFECT OF EXTERNAL FIELDS ACKNOWLEDGEMENTS... 

Fig. 4.10. Fundamental absorption bands in III-V compounds (after Stuke (1970)).

This point of view is fully confirmed by the changes in the fundamental absorption spectrum occurring when long-range order disappears. In Figures 4.19, 4.20 and 4.21 we see that the fundamental absorption bands are often smooth single bands for some materials (Figures 4.22, 4.23, 4.24) there are 2 smooth bands. 

The fundamental absorption bands were determined from the measurements of the reflectivity at normal incidence and the subsequent use of Kramers-Kronig analysis (cf. e.g. Tauc (1965)). To be able to perform this analysis it is necessary to make some assumptions about the extrapolation of the reflectivity curve above the maximum measured frequency to infinity. The shape and position of the sharp structure observed in crystal spectra is little affected by various choices of this extension. However, the position of a smooth band as observed in amorphous semiconductors may be shifted differently with different extrapolations. The data might be also affected by the surface condition. To be sure about the absorption shift, Tauc and Abraham (1970) determined the absorption constant in a-Ge by a different method, the measurement of the transmission of thin a-Ge films, and confirmed the results obtained by Kramers-Kronig analysis. 

The observed shift makes the interpretation of the fundamental absorption band non-trivial. Tauc et al (1965) suggested that the absorption band... 

Fig. 4.19. Fundamental absorption bands of a-Ge and c-Ge (after Spicer and Donovan (1970a)).

Fig. 4.21. Fundamental absorption bands of a-CdGeAs and c-CdGeASj (after Tauc et al (1968) cf. also Gorjunovaeffl/ (1970)).

---