H band

There are two main kinds of dye aggregates, characterized by their typical spectral properties J-aggregates and H-aggregates. The absorption band maximum (f-band) of the J-aggregates is shifted bathochromicaHy with respect to that of an isolated molecule (M-band) the absorption maximum of the H-aggregates is shifted hypsochromicaHy (H-band). The dyes can also form dimers with a shorter absorption wavelength (D-band). 

The relative importance of structures 130 and 131 have long been discussed for the dye indanthrone. Initially, the infrared spectrum was considered to favor 131 ° because a vN—H band could not be found. However, this interpretation has been questioned, and recently the predominance of structure 130 was established by Weinstein and MerritP on the basis of the following evidence (a) a... 

The N—H functional group of amines is also easy to spot in the IR, with a characteristic absorption in the 3300 to 3500 cm-1 range. Although alcohols absorb in the same range, an N—H absorption is much sharper and less intense than an O-H band. 

The IR spectra show two i/(Os-H) bands (1950 and 1920 cm-1 for PR3 = PMe2Ph) this supports a cw-structure (a frans-structure would only give one band), a conclusion supported by the NMR data. These compounds, therefore, have rigid structures. 

These have simple IR spectra with only one KOs-H) band. 

Under 50 mbar of H2 and 50 °C, SnBu4 reacts selectively on the Pt surface to form surface complexes of average formula Pts[SnBux] /. The empirical formula (values of x and y) depend on the reaction time and on the Snint/Pts ratio (Fig. 6). Note that under these conditions SnBu4 does not chemically react with the silica surface, but it is fully physisorbed on the support [114]. In fact, when silica is contacted with SnBu4, IR spectroscopy shows a shift of the v(0 - H) band of silica to lower wave numbers, i.e. from 3747 cm to ca. 3700 cm which results from van der Waals interactions between the hydroxyl groups of the support and the butyl chains of adsorbed SnBu4 (Scheme 32). 

The material balance is consistent with the results obtained by OSA (S2+S4 in g/100 g). For oil A, the coke zone is very narrow and the coke content is very low (Table III). On the contrary, for all the other oils, the coke content reaches higher values such as 4.3 g/ 100 g (oil B), 2.3 g/ioo g (oil C), 2.5 g/ioo g (oil D), 2.4/100 g (oil E). These organic residues have been studied by infrared spectroscopy and elemental analysis to compare their compositions. The areas of the bands characteristic of C-H bands (3000-2720 cm-1), C=C bands (1820-1500 cm j have been measured. Examples of results are given in Fig. 4 and 5 for oils A and B. An increase of the temperature in the porous medium induces a decrease in the atomic H/C ratio, which is always lower than 1.1, whatever the oil (Table III). Similar values have been obtained in pyrolysis studies (4) Simultaneously to the H/C ratio decrease, the bands characteristics of CH and CH- groups progressively disappear. The absorbance of the aromatic C-n bands also decreases. This reflects the transformation by pyrolysis of the heavy residue into an aromatic product which becomes more and more condensed. Depending on the oxygen consumption at the combustion front, the atomic 0/C ratio may be comprised between 0.1 and 0.3 ... 

NaturgemaB ist auch die Erkennung einer Acetylen-H-Bande eine wertvolle Moglichkeit der IR-Spektroskopie. In Abb. 7 ist das IR-Spektrum eines Polyins mit freiem Acetylenwasserstoff wiedergegeben. 

Figure 4. IR spectra in D -doped liquid Kr at -120°C of (OC) Cr(ol) and of the photolysis product (OC) Cr(ol)(D ) [ol = trans-cyclooctene]. D2 was used rather than H2 to avoid potential spectral overlap of any V(H-H) bands with bands due to the hydrocarbon ligand.

The temperature effect on the absorption spectra is also shown in Fig. 2. One can see that the peak position and bandwidth of the P band increase with temperature, while in other bands (like the B and H bands) only its bandwidths show a positive temperature effect. It is important to note that even though the RC is a complicated system, its spectra are relatively simple and its bandwidth is not particularly broad. The above features of absorption spectra of RCs need to be taken into account when analyzing the observed absorption spectra. 

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