Spectra changes, absorption

The amount of a particular component in a sample can be monitored by examining the height of a spectral absorption peak The reduction of an aldehyde to an alcohol would show up as a decrease in line intensity for the carbonyl and an increase for the hydroxyl peaks in the spectrum. Changes in the relative importance of different relaxation modes in a polymer can also be followed by the corresponding changes in a mechanical spectrum. 

Odontosyllis luciferin is colorless and shows an absorption maximum at about 330 nm in aqueous ethanol (Figs. 7.2.1 and 7.2.2), and it undergoes various spectrum changes upon spontaneous oxidation... 

A broad absorption spectrum of t,t,t-TPCB" was observed at 77 K, at 400-670 nm with a peak at 480 nm, and collapsed without any particular spectral change upon warming up to 90 K (Fig. 4). However, the spectrum changed to have clear peaks at 485 and 780 nm upon photoirradiation at 77 K (Fig. 4a). The absorption spectrum then changed to have a peak at 550 nm upon warming. The difference spectrum, obtained by subtracting the spectra both before and after warming, clearly indicates the collapse of the peak at 485 nm and the formation of bands at 370, 550, and 770 nm (Fig. 4b). 

Figure 4. IR absorption spectrum change of PIQ after high-temperature heating (a) as prepared and (b) after heating in nitrogen at 450°C for 5 h.

Many pH indicators owe their utility to their absorptions in the visible region of the UV-Vis spectrum. Changes to the pH lead to changes in the indicator chromophore, and result in reliable colour changes at predictable pH values. One such example is that of phenolphthalein, which is a phenol and can be deprotonated at elevated pH to give the anion (Scheme 2.4), extending the chromophore and leading to a... 

In the following pages we describe our extensions in each of the above areas to afford sulfonic acid derivatives, carbon-carbon bond formation and carbonylation of PCTFE. The most direct indication of substitution is found through examination of the absorption IR spectrum. Changes in the spectrum of native PCTFE (see Figure 1) include loss of the carbon chlorine stretch and introduction of new stretching frequencies. 

If the terminal groups contain a local level lying near the frontier polymethine level, then a new transition type involving this level, ie, the local or quasilocal electron transition (LET), can appear. It has been proposed to consider the terminal groups as local chromophores (26). LET can have lower energy than PMET, for example, in such dyes as (12) (28). In this case the absorption spectrum changes essentially (Fig. 3) and the short-wavelength band is narrower and appears to be a typical polymethine one. 

Since all of the chalcogenometalates have strong and characteristic absorption bands in the UV-vis region, the reactions in which they are formed and decomposed can be readily followed by spectrophotometric methods. When hydrogen sulfide is passed into an aqueous solution of an oxometalate the electronic spectrum changes, the bands of all the species M04 S (n = 1-4 M = V, Mo, W, Re) appearing in succession (cf Figure 3 of Chapter 16.1). 

Figure 8 Schematic representation of how the Zeeman effect works. In the top sketch, no field is applied (normal A AS) and the absorption profile (—) overlaps the emission profile (—). In the lower sketch, with the field on, the absorption spectrum changes, and the

As we indicated in Chapter 4 (Section 4.1 D), both the quantity and the quality of radiation change as a function of depth in water wavelengths near 500 nm penetrate the deepest. For instance, only about 10% of the blue and the red parts of the spectrum penetrate to a depth of 50 m in clear water, so chlorophyll is not a very useful light-harvesting pigment below that depth (see Fig. 5-3 for a chlorophyll absorption spectrum). Changes in the spectral quality (relative amounts of various wavelengths) with depth can affect the... 

When the complex 3a with triethylphosphite as a monodentate ligand was irradiated at 365 run in MeCN, the UVA is absorption spectrum changed with some isosbestic points (Fig. 8). This photochemical reaction gave exclusively cis, ra7rs-[Re(bpy)(CO)2 P... 

The absorption band at 430 nm is seen as a shoulder of the stronger band at 370 nm. Upon irradiation of crystalline DSP with 430 nm monochromatic light, the UV absorption spectrum changes, and new peaks appear at 350 nm and 290 nm (Fig. 6). The IR absorption band at 970 cm-1 corresponding to vCH of a trans HC=CH bond gradually decreases, and then reaches a constant level at about one fifth of the initial values (Fig. 7). At this stage, the monomer in KBr pellets has almost vanished. 

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