Near-infrared band assignments

There are many current techniques used for assisting in near-infrared band assignments, including Darling-Dennisotf resonance, deuteration, polarization, and two-dimensional (2-D) correlation spectroscopy. The scope of this book is practical rather than theoretical, and so the techniques are mentioned here for further investigation by the reader. 

Characteristic for the Mn111 and Fe111 porphyrins of the type M(P)X (Table 18) are the weak absorptions in the near infrared (Band I in Fig. 2). The origin of these bands, as well as those in the visible and UV region is still in question. As mentioned in Sect. 4.1, assignment of the absorption bands has been based on interactions between normal porphyrin it - jt transitions and porphyrin it -> metal dff charge... 

In the dilute solution spectrum of methanol, three sharp peaks are observed superimposed on the broader continuum. These can be seen clearly in Figure 5.3. The sharp peaks have been assigned to OH stretch plus CH bending at 5090 cm" (1965 nm), OH stretch plus OH bending at 4960 cm" (2017 nm), and OH stretch plus CO stretch at 4710 cm" (2124 nm). There is also a second combination of OH-stretching and a different OH-bending mode at about 3970 cm (2520 nm). These sharp peaks are at different positions in other alcohols. In the neat spectrum, these peaks are seen as only one broad band centered at about 4770 cm" (2100 nm). In the mid-infrared, a diffuse OH association band related to deformation occurs at about 1420 cm" which can account for the 4770-cm near-infrared band (1420 cm" + 3350 cm" = 4770 cm". The diffuse mid-infrared band is said to disappear in dilute solutions of alcohols, where hydrogen... 

A related complex is [(NH3)5Ru(bqd)Ru(NH3)5] (bqd = p-benzoquinone diimine) [102], Also here there is complete delocalization. The absorption spectrum of this ion is given in Fig. 17. It consists of an extremely intense band in the visible = 108.000 cmand a much weaker one in the near infrared (en,ax — 1000 cm ). The latter has been assigned to the MMCT... 

A more detailed spectroscopic study of the T Cl ion has been reported by Cotton et al. (70). Of particular interest is the band in the near infrared, between 6000 and 8000 cm, which the authors assign as the 6 - 6 transition. Values for absorption energies were calculated from SCF-Xa analysis, and numerical agreement with assigned bands was superior to the agreement attained in related even-electron calculations for Re2Cll (194) and Mo2Clg (199). 

Here the constant b was assumed to have the same value for both the E and E states. This assumption is consistent with transition [2] being a narrow peak while transitions [3] and [4] are broader bands, as the structure of the near-infrared absorption of CuIJY demonstrates (Fig. 9). Transitions [2], [3], and [4] are assigned the observed frequencies 10900, 12700, and 14650 cm l, and transition [1] will be shown to be below 1000 cm-l. The energy difference between transitions [2] and [3] depends only on the Jahn-Teller coupling constant, which is determined to be b = 3600 cm- from the observed frequencies. The spin-orbit coupling constant X is equal to 829 cm l for the free Cu11 ion (23), but in Cu11 complexes assumes the value close to 400 cm l. In the present analysis the band centers are insensitive tj various choices of,X. With X = 400 cm and b2 = 3600 cm, the... 

In other cases, a baseline corrected peak height for a particular absorber may be employed as a term in the equation. In such a case, the wavelength difference on either side of a peak maximum will affect the contribution of that complex term. That increment or gap, in fact, under such circumstances becomes a part of the calibration. It is as important a contribution to the calibration as the coefficients on the wavelength terms. In this correlation spectroscopy, classical band assignments are not always possible. Little specific near-infrared literature exists in advance of most applications and it is not always possible to predict which wavelengths will produce the best linearity and the best sensitivity for a given analytical problem. In the empirical approach a variety of statistical treatments have been attempted. By far the most... 

The best example of a study of this type of intermediate is found in the oxidation of CO over a nickel-nickel oxide catalyst 24). The latter term is used because there is doubt as to the specific nature of the catalyst surface. The spectrum in Fig. 14 was obtained during the oxidation of CO over nickel-nickel oxide at 35° C. The band at 4.56 u is tentatively attributed to an intermediate complex having the structure Ni- 0 C rr.O. The bands at 6.5 and 7.2 u are due to C02 chemisorbed on the catalyst surface. This C02 is considered to be adsorbed product rather than as a reaction intermediate because these bands remain after the reaction is completed. The 4.56- u band in Fig. 14 is attributed to the asymmetrical 0—C—0 vibration rather than to the C—O vibration of chemisorbed CO. This interpretation implies that there should be a second band due to the symmetrical vibration. The symmetrical 0—C—O vibration of C02 produces a Raman band at 7.2 ju. The symmetrical 0—C—0 vibration of Ni - -O—C=0 would be expected to produce an infrared band near 6 or 7 u- Thus far this band has not been observed. This failure is not considered a serious obstacle to the structure assignment,... 

Carbonate band assignment has been more difficult in Raman spectra than in the infrared [15] because of near overlap of the major carbonate Vi mode at 1070cm-1 with a component of phosphate V3 at 1076cm-1 in carbonated apatites [16]. These bands have earlier been reported as coincident [17] or have been assumed to be a single broad carbonate band [18]. Most investigators have used the ratio of the carbonate Vi band/phosphate Vi band as a measure of the carbonate/phosphate ratio. It is likely that in many cases this error is small, but for lightly carbonated mineral, typically freshly precipitated mineral, the error may be important. Remeasurement or reinterpretation of some Raman spectroscopic data may be needed. 

The radical anion Cw, can also be easily obtained by photoinduced electron transfer from various strong electron donors such as tertiary amines, fer-rocenes, tetrathiafulvalenes, thiophenes, etc. In homogeneous systems back-electron transfer to the reactant pair plays a dominant role resulting in a extremely short lifetime of Qo. In these cases no net formation of Qo is observed. These problems were circumvented by Fukuzumi et al. by using NADH analogues as electron donors [154,155], In these cases selective one-electron reduction of C6o to Qo takes place by the irradiation of C6o with a Xe lamp (X > 540 nm) in a deaerated benzonitrile solution upon the addition of 1-benzyl-1,4-dihydronicoti-namide (BNAH) or the corresponding dimer [(BNA)2] (Scheme 15) [154], The formation of C60 is confirmed by the observation of the absorption band at 1080 nm in the near infrared (NIR) spectrum assigned to the fullerene radical cation. 

The near-infrared PL15 at 0.8 eV (below the bulk Si band gap) exhibits complex nonexponential dynamics, with a wide distribution of decay times, and has been assigned to deep level transitions associated with dangling bonds on the surface of the Si nanocrystallites.54... 

Water solubilized by RMs in hydrocarbon solvents by different surfactants (anionic, cationic and zwitterionic) exhibits two absorption bands in the near infrared spectral region (5200-4700 cm 1) due to water populations (Sunamoto et al., 1980), one assigned to the surfactant polar heads and the other to water dispersed in the bulk phase. Three methods have been proposed to evaluate the acidity in the water pool of soft-core of reverse micelles ... 

Since isomerically pure polymers were not available, three different kinds of BR, each relatively high in one of the three kinds of base units were used as standards [35]. The band near 1308 cm 1 was identified [38,39] with the cis isomer and used for analyses [43]. The 1308 cm 1 band is weak and relatively broad, with the appearance of an unresolved doublet (1306,1311 cm 1). The cis band at 730 cm 1 is more frequently used in spite of some difficulties. Relatively pure, crystalline stereoregular polymers have been prepared and structures were determined by X-ray diffraction for cis [44], trans [45] and syndiotactic vinyl [46] and isotactic vinyl [47]. Infrared spectra [48-50] have been published for the four stereoregular polybutadienes, with detailed analyses of the spectra and band assignments for cis [51], trans [51] and syndiotactic vinyl [51] polymers. For the spectrum of isotactic vinyl BR, bands at 1232, 1225, 1109, 943, 876, 807 and 695 cm"1... 

The electronic spectra of tetrahedral complexes consist in general of two groups of bands, one in the near infrared, the other in the visible region. They can be assigned,... 

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