Ring breathing mode

Three /3-CH modes corresponding to in-plane C—H deformations are also observed (Table 22) and are probably best depicted as in (27), (28) and (29), although those for pyrrole will be modified as a result of interaction with the in-plane N—H deformation. The skeletal ring breathing mode (30) observed at ca. 1137 cm for 2-substituted pyrroles and... 

In comparison to 1 and 2, the SERS spectra of 3-pyridine-carboxaldehyde (3) are relatively featureless (8). The spectra are dominated by the symmetrical ring-breathing mode at 1030 cm 1 but the features associated with the unprotonated species (about 1600 cm ) and the protonated species (about 1640 cm 1) are definitely present along with a weak carbonyl band at about 1710 cm . The variation in the relative population of protonated species is as expected (Figure 5) though a detailed analysis reveals some surprises. As can be seen in Figure 5, about equal intensities of the 1600 and 1640 cm bands are obtained at pH = 3.86, near the pKa (3.73 (9)). However, the band associated with the unprotonated pyridine persists at pH = 1.3, where less than 1J of the solution species remains unprotonated. 

Raman spectra obtained on concentrated protein solutions (ca. 20 mM) are dominated by contributions from the repeating amide group of the polypeptide backbone and from the sldechalns of aromatic amino acids (6). Phenylalanine and tryptophan exhibit particularly Intense ring breathing modes at 1006 and 1014 cm, respectively. An additional strong peak due to tryptophan Is typically observed at 760 cm ... 

In 2-substituted thiophenes these bands are found in the ranges 1537-1509, 1444-1402, 1365-1339 and 1258-1220 cm-1, along with hydrogen in-plane absorption at 1086-1077 and 1053-1031 cm "1, and hydrogen out-of-plane absorption at 938-905 and 863-841 cm-1 as well as a ring breathing mode at 839-790 cm-1 (59JCS3500). 

The V4 is the strongest when RR spectra are obtained with Soret band excitation. As shown in Table 4-5, it is mainly due to v(Ca—N), a totally symmetric pyrrole ring breathing mode. This band is well known as an oxidation state marker. It is at 1,355cm 1 for Fe(II) and at 1.370cm-1 for Fe(III) with relatively small dependence on spin state. For example, the order of the V4 are... 

In the benzene data (49) in Fig. 16, the 606 cm-1 ring deformation mode has a two-part rise. The first part mirrors the 10 ps decay of the C-H stretch. The second part mirrors the 40 ps decay of intermediate energy vibrations such as the ring breathing mode at 992 cm-1. The decay lifetime is difficult to determine accurately because it is so slow, but is estimated at 100 ( 20) ps. 

The jSCH modes are more variable and only the principal bands are listed. The last two bands, at ca. 1150 and 1050 cm , could be ring breathing modes. 

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