IR-and Raman Spectroscopy

Characteristic bands occur in the 1300-1000 cm region for 3,4- and 3,5-disubstituted isoxazoles (7i PMh(4)265, p. 330), while bands below 1000 cm contain modes for most substitution patterns (71PMh(4)265, p. 332). Total assignments for isoxazole and isoxazole-d have been made (63SA1145, 7lPMH(4)265,p. 325) and some of the thermodynamic functions calculated (68SA(A)361, 71PMH(4)265,p.330). 

The IR (and Raman) spectra of 1,2-benzisoxazole and 2,1-benzisoxazole have been recorded and their fundamental and combined vibrations assigned (80MI41604). Similar studies have been carried out with 2,1-benzisoxazolium salts (74DIS(B)147, 71JOC1543). 

The keto-enol tautomerism of 1,2-benzisoxazoles has been examined and the existence of either form can be postulated on the basis of reactivity. IR analysis on the solid indicates the exclusive existence of the enol form, while in CHCI3 solution both appear to be present (71DIS(B)4483). 

Further details of instrumentation are given in Chapter 3 and Appendix 1. 

Spell and Eddy [3] described infrared (IR) spectroscopic procedures for the determination of up to 500 ppm of various additives in polyethylene (PE) pellets following solvent extraction of the additives at room temperature. They showed lonol (2,6-di-ter -butyl-p-cresol) and Santonox R (4,4 -thio-bis(6-ter -butyl- /-cresol)) are extracted quantitatively from PE pellets by carbon disulfide in 2-3 hours and by isooctane in 50-75 hours. The carbon disulfide extract is suitable for scanning in the IR region between 7.8 and 9.3 (xm, while the isooctane extract is suitable for scanning in the UV region between 250 and 350 nm. 

Miller and Willis [4] obtained IR spectra of antioxidants in polymer films. They compensated with additive-free polymer in the reference beam. IR spectroscopy is more specific than UV spectroscopy [5-7]. 

Patticini [8] has described an IR method for the determination of 1-8% of mineral oil in polystyrene (PS). In this method the PS sample is dissolved in carbon tetrachloride, together with known mineral oil standards. The solutions are evaluated by measurements made between 3100 and 3000 cm using a spectral subtraction technique. 

Fourier transform near-IR Raman spectroscopy (400-10,000 cm ) is useful for the examination of additives in polymer extracts [9]. 

Deviations from the computed values result, on one hand, from the calculation method itself, and on the other hand should the actual structure of the IR-spec-trum be influenced by the interaction between individual shells of the onion that alter the vibrational behavior. 

The Raman spectrum of carbon onions is rather simple, too. Essentially, there are two bands situated in the regions about 1350 and 1580cm . In principle, a Raman signal should be expected for every single shell. These signals are, however, presumed to lie in close proximity and thus a cumulative spectrum with broad signals is obtained. 

The additional band at 1572 cm can be assigned to the onion structure. It originates from the in-plane vibration of the six-membered rings (E2g-mode) of the 

The Raman spectrum of carbon onions exhibits further, less intensive signals at 250, 450, 700, 861, and 1200 cm . These as well become visible due to a breach of the selection rules that is associated with the bent graphene layers. 

An important task for theory in the quest for experimental verification of N4 is to provide spectral characteristics that allow its detection. The early computational studies focused on the use of infrared (IR) spectroscopy for the detection process. Unfortunately, due to the high symmetry of N4(7)/) (1), the IR spectrum has only one line of weak intensity [37], Still, this single transition could be used for detection pending that isotopic labeling is employed. Lee and Martin has recently published a very accurate quartic force field of 1, which has allowed the prediction of both absolute frequencies and isotopic shifts that can directly be used for assignment of experimental spectra (see Table 1.) [16]. The force field was computed at the CCSD(T)/cc-pVQZ level with additional corrections for core-correlation effects. The IR-spectrum of N4(T 2 ) (3) consists of two lines, which both have very low intensities [37], To our knowledge, high level calculations of the vibrational frequencies have so far only been performed 

Computed harmonic (fi ) and fundamental (v) frequencies, IR and Raman intensities and bond length for N4(7 t/) (l)a  

Raman spectroscopy provide complementary information to IR in that bands that are inactive in IR often are active in Raman, and vice versa. The Raman spectrum of 1 consists of three bands with relatively high intensity [37, 38], while the corresponding spectrum for 3 has two strong and one weaker line [37]. Thus, in contrast to IR, Raman provides a tool for fingerprinting of both molecules even without the use of isotopic labeling. In addition, the detection limit is expected to be lower in Raman than IR due to the very low intensities of the IR transitions. We have recently estimated the detection limit for 1 in liquid and solid nitrogen based on experimental measurements and computed Raman intensities for 1 and N2. The following expression was used to compute the detection limit  

Symmetry Scaled B3LYP/6-311G b (0 CAS(12,12)/ cc-pVTZc 00 CCSD(T) cc-pVTZc CO B3LYP/6-311G Intensities1 IR Raman  

---

Vibrational spectroscopy provides detailed infonnation on both structure and dynamics of molecular species. Infrared (IR) and Raman spectroscopy are the most connnonly used methods, and will be covered in detail in this chapter. There exist other methods to obtain vibrational spectra, but those are somewhat more specialized and used less often. They are discussed in other chapters, and include inelastic neutron scattering (INS), helium atom scattering, electron energy loss spectroscopy (EELS), photoelectron spectroscopy, among others. 

Both infrared and Raman spectroscopy provide infonnation on the vibrational motion of molecules. The teclmiques employed differ, but the underlying molecular motion is the same. A qualitative description of IR and Raman spectroscopies is first presented. Then a slightly more rigorous development will be described. For both IR and Raman spectroscopy, the fiindamental interaction is between a dipole moment and an electromagnetic field. Ultimately, the two... 

Time-resolved spectroscopy has become an important field from x-rays to the far-IR. Both IR and Raman spectroscopies have been adapted to time-resolved studies. There have been a large number of studies using time-resolved Raman [39], time-resolved resonance Raman [7] and higher order two-dimensional Raman spectroscopy (which can provide coupling infonuation analogous to two-dimensional NMR studies) [40]. Time-resolved IR has probed neutrals and ions in solution [41, 42], gas phase kmetics [42] and vibrational dynamics of molecules chemisorbed and physisorbed to surfaces [44]- Since vibrational frequencies are very sensitive to the chemical enviromnent, pump-probe studies with IR probe pulses allow stmctiiral changes to... 

Selected physical properties of chloroprene are Hsted in Table 1. When pure, the monomer is a colorless, mobile Hquid with slight odor, but the presence of small traces of dimer usually give a much stronger, distinctive odor similar to terpenes and inhibited monomer may be colored from the stabilizers used. Ir and Raman spectroscopy of chloroprene (4) have been used to estimate vibrational characteristics and rotational isomerization. 

Further benzofuroxan spectra are reported by Gaughran, Picard, and Kaufman, who compare them with benzofurazans, by Boyer et al., who find similarities with furoxans and nitroso compounds, and by others. Hexanitrosobenzene was shown by IR and Raman spectroscopy to exist in the benzotrifuroxan structure. ... 

Among the techniques mentioned previously, XPS has the greatest impact on polymer surface analysis. A major additional source of chemical information from polymers comes from IR and Raman spectroscopy methods, These vibrational data can be obtained from the bulk and the surface region, although the information depth is much greater than with AES, XPS, or ISS. 

However, a recent study of the lithium ion complexation with N-labelled polyphosphazenes, including N-MEEP, was performed by Luther [600]. The data obtained for the MEEP/LiSOjCFj system by NMR, IR and Raman spectroscopies do not support that assumption, and show that the coordination of the lithium ion also occurs with the nitrogen nuclei. 

Wartewig, S., IR and Raman Spectroscopy, Eundamental Processing, Spectroscopic Techniques An Interactive Course, WUey-VCH, Weinheim, 2003, 175. 

The driving force for the temperature-dependent spin crossover (SCO) is the entropy difference between the HS and the LS isomers which arises mainly from a shift of the vibrational frequencies when passing from the HS to the LS state [97-99]. This frequency shift has been studied by IR- and Raman-spectroscopy and recently also by NIS [23, 39, 87]. The NIS method is isotope ( Fe) selective and, therefore, its focus is on iron-ligand bond-stretching vibrations which exhibit the most prominent contribution to the frequency shift upon SCO [87]. 

The vibrational modes of the LS and HS isomers of the SCO complex [Fe (phen)2(NCS)2l (phen = 1,10-phenanthroline) have been measured by NIS (Fig. 9.38a), IR- and Raman-spectroscopy, and the vibrational frequencies and normal modes were calculated by DFT methods [44]. The calculated difference ASvib = 57-70 J moP depending on the method) is in qualitative agreement with the experimentally derived values (20-36 J mol K ). 

In summary, the combined experimental (NIS, IR- and Raman-spectroscopy) and computational (DFT) approach has enabled the identification of the vibrational modes that contribute most to the entropic driving force for SCO transition. 

IR and Raman spectroscopy have been commonly used and, for example, the effects of pressure on the Raman spectrum of a zinc compound with a N2C12 coordination sphere around the metal, have been investigated.28 IR spectroscopy has been utilized in studies of the hydration of zinc in aqueous solution and in the hydrated perchlorate salt.29 Gas phase chemistry of zinc complexes has been studied with some gas phase electron diffraction structures including amide and dithiocarbamate compounds.30-32... 

Whereas several techniques may thus be used to study a certain characteristic of a polymer sample, for instance IR and Raman spectroscopy and X-ray diffraction as well as NMR may be used to determine or infer the crystallinity level of a sample, different techniques work differently and therefore usually do not measure the same. What this means is that crystallinity levels obtained from the same sample may differ when a different technique is applied, see, for example, ref. [23] and chapter 7 and references therein. However, these differences do not necessarily imply one technique being better than another. In fact these differences may contain useful information on the sample (see, for example, ref. [25]). 

IR and Raman spectroscopy can fulfill these requirements and they are also robust enough for in situ silicate analysis in plant reactors [7]. Both of these techniques have been used for identifying the symmetric (s) and asymmetric (as), stretching (va, vas) and bending (5a, 5as) O-Si-O vibrations in aqueous alkaline silicate solutions which are the cheapest hence most frequently used ingredients for zeolite synthesis [8, 9 and references herein]. However, this information has to be "translated" into siloxane ring... 

In the present study low temperature (373 K) hydrothermal technique has been employed for the synthesis of Na8[GaSi04]6(C104)2, containing perchlorate as a guest anion. The product obtained was characterized by x-ray powder diffraction, IR and Raman spectroscopy. The product crystallizes with the cubic sodalite in the space... 

Vibrational spectroscopy measures and evaluates the characteristic energy transitions between vibrational or vibrational-rotational states of molecules and crystals. The measurements provide information about nature, amount and interactions of the molecules present in the probed substances. Different methods and measurement principles have been developed to record this vibrational information, amongst which IR and Raman spectroscopy are the most prominent. The following focuses on these two techniques, the corresponding instrumentation and selected applications. 

Most chemists tend to think of infrared (IR) spectroscopy as the only form of vibrational analysis for a molecular entity. In this framework, IR is typically used as an identification assay for various intermediates and final bulk drug products, and also as a quantitative technique for solution-phase studies. Full vibrational analysis of a molecule must also include Raman spectroscopy. Although IR and Raman spectroscopy are complementary techniques, widespread use of the Raman technique in pharmaceutical investigations has been limited. Before the advent of Fourier transform techniques and lasers, experimental difficulties limited the use of Raman spectroscopy. Over the last 20 years a renaissance of the Raman technique has been seen, however, due mainly to instrumentation development. 

A brief description of IR and Raman theory will be presented so that a common understanding of the techniques is available to the reader. A complete description of the underlying theory to IR and Raman spectroscopy is outside the scope of this chapter, but can be obtained from the literature [1-5]. 

---