Main absorption

The BASF process uses /V-methy1pyrro1idinone as the solvent to purify acetylene in the cracked gas effluent. Alow pressure prescmbbing is used to remove naphthalenes and higher acetylenes. The cracked gas is then compressed to 1 MPa (10 atm) and fed to the main absorption tower for acetylene removal. Light gases are removed from the top of this tower. 

Absorption Refrigeration Systems Two main absorption systems are used in industrial application lithium bromide-water and ammonia-water. Lithium bromide-water systems are hmited to evaporation temperatures above freezing because water is used as the refrigerant, while the refrigerant in an ammonia-water system is ammonia and consequently it can be applied for the lower-temperature requirements. 

Regarding the characterization of corn cob xylan by Fourier-transform infrared (FT-IR) spectroscopy, two main absorption bands at 3405 cm-i and 1160 cm-i are revealed. They can... 

Solvent — The transition energy responsible for the main absorption band is dependent on the refractive index of the solvent, the transition energy being lower as the refractive index of the solvent increases. In other words, the values are similar in petroleum ether, hexane, and diethyl ether and much higher in benzene, toluene, and chlorinated solvents. Therefore, for comparison of the UV-Vis spectrum features, the same solvent should be used to obtain all carotenoid data. In addition, because of this solvent effect, special care should be taken when information about a chromophore is taken from a UV-Vis spectrum measured online by a PDA detector during HPLC analysis. 

As discussed in Sect. 1.2.3, it is usually not possible to distinguish ESA from 2PA with Z-scan experiments if they are performed with only one excitation pulsewidth. However, since ESA is not an instantaneous process as is 2PA, the pump-probe technique can be successfully used to verify the origin of the nonlinearity for the spectral regions close to the main absorption band. Figure 7 illustrates how the influence of the ESA can be distinguished from the 2PA with pump-probe experiments. The curve labeled (1) shows an instantaneous 2PA response without ESA and the long-lived components of the transmittance change seen in (2) and (3) are due to ESA. 

Introduction of the acceptor squaraine and tetraone bridges to the conjugated chain causes BLA in the bridges resulting in a blue shift of the main absorption... 

The absorption spectra for all these dyes are composed of intense cyanine-like bands attributed to the, S 0 S) absorption, with the main absorption peaks shifted by fslOO nm to longer wavelengths upon lengthening of the main conjugation... 

In order to determine the structural factors maximizing 2PA cross section values, we analyze (8) from Sect. 1.2.1. For all cyanine-like molecules, symmetrical and asymmetrical, several distinct 2PA bands can be measured. First, the less intensive 2PA band is always connected with two-photon excitation into the main absorption band. The character of this 2PA band involves at least two dipole moments, /

symmetry forbidden for centro-symmetrical molecules, such as squaraines with C, symmetry due to A/t = 0, and only slightly allowed for polymethine dyes with C2V symmetry (A/t is small and oriented nearly perpendicular to /t01). It is important to note that a change in the permanent dipole moment under two-photon excitation into the linear absorption peak, even for asymmetrical D-a-A molecules, typically does not lead to the appearance of a 2PA band. 2PA bands under the main absorption peak are typically observed only for strongly asymmetrical molecules, for example, Styryl 1 [83], whose S0 —> Si transitions are considerably different from the corresponding transitions in symmetrical dyes and represent much broader, less intense, and blue-shifted bands. Thus, for typical cyanine-like molecules, both symmetrical and asymmetrical, with strong and relatively narrow, S (I > S) transitions, we observe... 

It has been shown that the irradiation by light in the main absorption band may either accelerate the oxidation of CO [the positive photocatalytic effect (11, 50-56) 4 or decelerate it [the negative photocatalytic effect (11, 53)]. The magnitude and sign of the effect are determined by experimental conditions. 

Formation of these dinuclear mercury derivatives is accompanied by a red shift of the absorbance of the bis(alk-ynyl) backbone. For example, conversion of 2,7-bis(alkynyl)fluorene into the corresponding bis(methylmercury) derivative 50 leads to a shift of the main absorption band of the bis(alkynyl) backbone from 505 to 567 nm. Similar results have been obtained for 51-56.67 68... 

Interestingly, the UV maxima of the above dialkyl triafulvenes are only slightly influenced by the polarity and hydrogen-bonding capability of the solvent. In the cyclic triafulvene 195, countercurrent solvent shifts for the two main absorptions are observed. 

On the other hand in the exciton description occasionnally adopted by some authors to interpret the main absorption peak in the polydiacetylenes one finds x " negative and its values two orders of magnitude lower than expression 6 since electron correlation (28) is essential in the exciton model, the calculation of even the simplest optical properties becomes prohibitively complicated and the physical insight is obscured. 

Connors and Jozwiakowski have used diffuse reflectance spectroscopy to study the adsorption of spiropyrans onto pharmaceutically relevant solids [12]. The particular adsorbants studied were interesting in that the spectral characteristics of the binary system depended strongly on the amount of material bound. As an example of this behavior, selected reflectance spectra obtained for the adsorption of indolinonaphthospiropyran onto silica gel are shown in Fig. 1. At low concentrations, the pyran sorbant exhibited its main absorption band around 550 nm. As the degree of coverage was increased the 550 nm band was still observed, but a much more intense absorption band at 470 nm became prominent. This secondary effect is most likely due to the presence of pyran-pyran interactions, which become more important as the concentration of sorbant is increased. 

CL as an analytical tool has several advantages over other analytical techniques that involve light (mainly absorption spectroscopy and fluorometry) high detectability, high selectivity, wide dynamic range, and relatively inexpensive instrumentation. 

The crystal violet ion has a main absorption band at about 5900 A, and another so close to it as to appear to be a shoulder on the main band. As the temperature is raised the main band shrinks while the shoulder becomes more prominent. This is interpreted as due to the increased conversion of the low energy form, responsible for the main absorption band, into the high energy form, responsible for the shoulder. The energy difference can be calculated by plotting the logarithm of the... 

Figure 8 in Ref. 213, reproduced on the right, displays diffuse-reflectance UV-Vis spectroscopic data obtained for titanium-substituted mesoporous (Ti-SBA-15) catalysts as a function of titanium content. Assign the main absorption feature observed at 200 to 220 mu and the shoulder seen at about 300 nm. What can we learn from this figure in terms of the different titanium species present on the solid ... 

The absence of coplanarity in both 1-phenyl- and 4-phenyldibenzo-thiophene degenerates their UV spectra to that of dibenzothiophene. In contrast, the main absorption bands of the 2- and 3-phenyl derivatives exhibit the expected bathochromic shift, indicating enhanced conjugation. Available data for the UV absorption of 1,2,3,4-tetraphenyl-dibenzothiophene is insufficient to correlate with these deductions. ... 

All varieties of color are mainly connected with two main absorption bands in the violet and yellow parts of the spectrum. The secondary bands are also present - in blue and green diapasons. The main absorption bands are connected with F and M-centers. The first one is anion vacancy, which traps electrons and the second is two neighboring anion vacancies with two trapped electrons. The short-wave band in fluorite is generated by mutual absorption of F and M-centers, while the long-wave band is connected with M-center absorption only. In the green varieties the REE (Sm ", Yb and Dy ) are also appreciable. Besides that, the centers O2, O3 and (Y, TR)02 sometimes have influence with resulting yellow and pink colors (Platonov 1979 Krasilschikova et al. 1986). 



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