Raman Lines Assignment

Raman lines assigned to the [AsF6]- anions evidence considerable departure from octahedral symmetry indicating significant Xe F—As bridging interaction. 

Suites 1 to VIII contain infrared frequencies corresponding to vibration-rotation bands of A, B, or (A-l-B) hybrid types and can thus be assigned to vibrations of A symmetry the corresponding Raman lines are generally polarized. 

The frequencies classified in suites IX and X belong to depolarized Raman lines and correspond to vibrations-rotation bands of the C type. They can be assigned to oscillations of A" symmetry. 

Fig. 6. Approximate form of vibration assigned to 1616 cm"1 Raman line. Also shown are the ring axes Ox Ox2Ox3. Reproduced from Polymer by permission of the publishers, Butterworth Co (Publishers) Ltd. (C)...

The infra-red measurements were of two types, normal-film measurements with the sample sandwiched between KBr plates, and tilted-film experiments with the sample sandwiched between 45° prisms of KBr, in each case with layers of Nujol to provide optical matching. Whereas the 1616 cm 1 Raman line occurs in a region well clear of other lines so that it was satisfactory to measure peak intensities, the infra-red spectrum of PET shows many overlapping bands. Accurate assessment of absorption intensities therefore requires the computer separation of the spectrum into a set of overlapping peaks (shown to be Lorentzian in profile) and a linear background. The procedures adopted and the band assignments are discussed in detail by Hutchinson et al. 6). 

The 520 nm absorption of S4 has also been observed in the spectrum of certain red-colored ultramarine samples [21] the assignment of this band to the C2V isomer of 4is supported by the simultaneously observed Raman line at 678 cm which represents the symmetrical stretching vibration of the terminal SS bonds of this molecule (see Table 1 below). 

Most of the many modes of a-Ss have been assigned to their symmetry class. However, some strong infrared absorptions (V4 240 cm V5 470 cm ) and weak Raman lines (Vn 250 cm ) as well as signals originating from accidental degeneracies (e.g., Vi, V5, and Vy at around 475 cm ) were difficult to assign. 

In a KI matrix the electronic absorption maximum of 82 - is observed at 400 nm, and the 88 stretching vibration by a Raman line at 594 cm k 83 shows a Raman line at 546 cm and an infrared absorption at 585 cm which were assigned to the symmetric and antisymmetric stretching vibrations, respectively. The bromides and iodides of Na, K, and Rb have also been used to trap 82 - but the wavenumbers of the 88 stretching vibration differ by as much as 18 cm- from the value in KI. The anion S3- has been trapped in the chlorides, bromides and iodides of Na, K, and Rb [120]. While the disulfide monoanion usually occupies a single anion vacancy [116, 122], the trisulfide radical anion prefers a trivacancy (one cation and two halide anions missing) [119]. 

The SO stretching vibration of S7O was observed at 1134 cm in the IR spectrum of a CS2 solution and at 1089/1102/1113 cm in the Raman spectrum of a soHd sample at -90 °C (the three very weak Raman lines probably originate from the intermolecular S—0 interactions). The two strongest Raman lines at 292 and 325 cm have been assigned to the SS stretching vibrations of the particularly weak bonds (see the bond distances in Fig. 2). 

The simplest intermediate of the nitrogen cation type is the nitronium ion, the active species in most aromatic nitration reactions. There is both cryoscopic and spectroscopic (Raman and infrared) evidence for its existence.802 On the other hand, it has a structure with quaternary rather than electron deficient nitrogen, a structure compatible with the centrosymmetric geometry demanded by the spectra. The Raman line at 1400 cm.-1 has been assigned to the totally symmetric vibration of the linear triatomic molecule. 

Raman scattering from crystalline S3, SCg, and cyclic selenium sulfides is very intense. The Raman spectrum of 1,2,3-86385 is shown in Fig. 3 as a typical example of the spectra of mixed Se Sg species. The first Raman spectra of liquid and solid sulfur-selenjum phases were reported in 1968 by Ward For a mixture of composition SCqojSo js he observed nine weak Raman lines not present in the spectrum of Sg and assigned them to different Se Sg (n = 0-4) molecules by comparison with the spectra of 8g and 8eg. According to the more recent calculations the assignment given in Table 4 is the most likely one. 

Table 4. The nine weak Raman lines of liquid and solid sulfur-selenium phase with composition S oo5 o95 assignment of the lines is given according to the calculations by the present...

Two Raman lines, either of which may be the Cr—Cr mode, have been observed at 340 and 400 cm-1 for [Cr2(mhp)4]. The former is preferred197 since the vibronic progression is 320 cm-1, and this is lower than earlier proposed.1 9 Others believe that this is a Cr—O or Cr—N totally symmetric stretch.198 The 22500 cm-1 band and the shoulder at 29 600 cm-1 are metal-dependent since they are intensified, and move together and to lower frequency from Cr to Mo to W. The shoulder at 29 600 cm-1 is assigned to the d—>x (Fli— 1E) transition.197... 

Theoretically, 0=s p =s 3/4, depending on the nature and symmetry of the vibration. Nonsymmetric vibrations give depolarizations of 3/4. Symmetric vibrations give p ranging from 0 to 3/4. Accurate values of p are important for determining the assignment of a Raman line to a symmetric or an asymmetric vibration. 

A variety of spectroscopic methods has been used to determine the nature of the MLCT excited state in the /ac-XRe(CO)3L system. Time-resolved resonance Raman measurements of /ac-XRe(CO)3(bpy) (X = Cl or Br) have provided clear support for the Re -a- n (bpy) assignment of the lowest energy excited state [44], Intense excited-state Raman lines have been observed that are associated with the radical anion of bpy, and the amount of charge transferred from Re to bpy in the lowest energy excited state has been estimated to be 0.84 [45], Fast time-resolved infrared spectroscopy has been used to obtain the vibrational spectrum of the electronically excited states of/ac-ClRe(CO)3(bpy) and the closely related/ac-XRe(CO)3 (4,4 -bpy)2 (X = Cl or Br) complexes. In each... 

For l,3,2(A2)-diazasilacyclopentene 83, the following Raman lines at 650, 991, 1178, 1566, 1573 cm-1 were reported in the solid state. The intensive doublet at 1566 and 1573 cm-1 was assigned to the (C=C) stretch vibration. The observed bathochromic shift of this band in the spectra of compound 83 compared to heterocyclic compounds having a tetravalent silicon, for example, 93, and the significant intensity enhancement of this band indicates cyclic conjugation in molecule 83 <2000JST329, 2004JA4114>. 

The interpretation of these Raman lines is not so straightforward, but Morrow and Hardin have presented in their publication a number of arguments that justify the assignments, summarized in table 11.1, for several chemical groups, chemisorbed on the silica surface. 

Raman spectra of thiocyanates appear to indicate that the ion is —S—C=N rather than S=C=N—, since a line assignable to the triple link and none for the double link was observed. Salts will be written as, e.g. KSCN and the ion as SCN-. 

It is convenient to discuss Raman investigations starting with item A. Tab. 4.8-2 lists prominent Raman lines for a number of CPs. The numbers in parantheses are the relative intensities on a scale of 1 to 5. Lines may be assigned to special vibrations according to the general rules outlined in earlier chapters of this book. Isotopic substitution in particular has been applied frequently and very successfully to these materials. In addition... 

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