Liquid-solution spectra

The value of Aj q obtained from Eq. 3 can be compared with that obtained from liquid solution spectra (see following two sections). 

Table III presents integral excess entropies of formation for some solid and liquid solutions obtained by means of equilibrium techniques. Except for the alloys marked by a letter b, the excess entropy can be taken as a measure of the effect of the change of the vibrational spectrum in the formation of the solution. The entropy change associated with the electrons, although a real effect as shown by Rayne s54 measurements of the electronic specific heat of a-brasses, is too small to be of importance in these numbers. Attention is directed to the very appreciable magnitude of the vibrational entropy contribution in many of these alloys, and to the fact that whether the alloy is solid or liquid is not of primary importance. It is difficult to relate even the sign of the excess entropy to the properties of the individual constituents.

The fluctuating cage model presented in Chapter 7 is an alternative. The idea came from comparison of the different kinds of absorption spectra of HC1 found in liquid solutions (Fig. 0.5). In SFg as a solvent the rotational structure of the infrared absorption spectrum of HC1 is well resolved [15, 16], while in liquid He it is not resolved but has... 

As was seen in the above discussion, normal Raman spectra are usually weak. In addition, in an NR solution experiment, the scattering comes from species in a c. 2 mm depth of liquid centred on the focused laser beam. Thus, the intensity of a spectrum from a monolayer of an adsorbed sample would be expected to be six orders of magnitude weaker than a NR solution spectrum, rendering NR too insensitive to be of use as an in situ probe. 

A problem with this method is the fact that mineral oil is a mixture of covalent substances (high-molecular-weight hydrocarbons) and its characteristic absorption spectrum will be found superimposed in the spectrum of the solid analyte, as with the solvents used for liquid solutions discussed previously. However, the spectrum is a simple one (Figure 8.24) and often does not cause a significant problem, especially if the solid is not a hydrocarbon. 

FTIR, like UV absorbance, refractive index, etc., is a technique for liquid solutions but has the advantage in that it is fast, allowing a complete spectrum to be obtained as a given mixture component elutes, making it an extremely powerful tool for qualitative analysis. 

Fig. 3.5. Fluorescence spectrum of benz[a]anthracene in n-heptane liquid solution at 300 K (top) and in n-heptane frozen solution at 15 l< (bottom). Concentration ...

The NH stretching band in triazole appears in the vapor phase at 3522 cm and in carbon tetrachloride at 3470 cm in the solid phase the NH absorption is a broad band at 2400-3300 cm (for 4-phenyl-triazole). The CH stretching frequency of 4- or 5-unsubstituted triazoles is at 3100-3140 cm (liquid phase).In-plane and out-of-plane deformation bands of the CH bond have also been distinguished at 1237 and 1076 cm (in the solution spectrum of 1,2,3-triazole), at 1290-1150 and 850-700 cm (for various substituted triazoles) and at 1149—1074 and 855-825 cm (for 2-aryltriazoles). ... 

At present it is universally acknowledged that TTA as triplet-triplet energy transfer is caused by exchange interaction of electrons in bimolecular complexes which takes place during molecular diffusion encounters in solution (in gas phase -molecular collisions are examined in crystals - triplet exciton diffusion is the responsible annihilation process (8-10)). No doubt, interaction of molecular partners in a diffusion complex may lead to the change of probabilities of fluorescent state radiative and nonradiative deactivation. Nevertheless, it is normally considered that as a result of TTA the energy of two triplet partners is accumulated in one molecule which emits the ADF (11). Interaction with the second deactivated partner is not taken into account, i.e. it is assumed that the ADF is of monomer nature and its spectrum coincides with the PF spectrum. Apparently the latter may be true when the ADF takes place from Si state the lifetime of which ( Tst 10-8 - 10-9 s) is much longer than the lifetime of diffusion encounter complex ( 10-10 - lO-H s in liquid solutions). As a matter of fact we have not observed considerable ADF and PF spectral difference when Sj metal lo-... 

In liquid solution the orientation of the ions is rapidly changing relative to the magnetic field. If the reorientation frequency is greater than the frequency width of the powder absorption line, the spectrum collapses to narrow lines and fits the isotropic spin Hamiltonian... 

Liquid-Ammonia Solutions—Spectrum and Photolysis of Potassium Amide. Figure 6 shows the spectrum of a bleached solution of potassium in ammonia, at —48°C. Only a single peak due to the amide is seen at 335 m/z before the ammonia cutoff. The molar decadic extinction coefficient, as determined by titration, is e = (1.0 =fc 0.2) X 104 at —48 ° C. and 335 m/z. (A careful Beer s Law check on the 335 m/z band has not yet been made.) The temperature coefficient of the peak is —20 cm. 1 deg. 1 (3), which is close to the value given above for the longwave band in decomposed ethylamine solution. 

Some improvement in resolution of the solution spectrum was obtained at the temperature of liquid nitrogen by Palmer and his coworkers 49). The maxima are observed at 412 mp, 456 mp, and 560 mp with a shoulder at 515 mp. The peak at 560 mp can only be detected as an extremely broad maximum in the room temperature spectrum. 

It is now realized that OH and RO radicals in liquid solution have an extremely short relaxation time due to various strong perturbations of the ir-levels (129). Their spectra are therefore too broad for detection, and this fact should be kept in mind when analyzing a complex ESR spectrum produced by the peroxide photolysis technique. Liquid photolysis of organic amines and hydrazines and the reaction of NC>2 with liquid olefins are known to produce nitrogen radicals. However, there is often a... 

For liquid solutions containing iron compounds or proteins, the Mossbauer-Lamb factor goes to zero, and therefore Fe Mossbauer spectroscopy on solutions is only possible in the frozen state. Since the natural abundance of Fe is only 2%, it is advisable to perform Mossbauer studies on solutions with Fe-enriched samples. For protein studies, Fe enrichment is essential. Typical sample volumes can range from 0.25-1.0mL. In some cases, frozen solution studies can be performed down to an Fe concentration of 0.1 mM, but taking a Mossbauer spectrum of such a sample can take weeks depending on the shape of the spectrum and the outcome is uncertain. Therefore, it is strongly recommended that the concentration of Fe be at least 1 mM. Samples with Fe concentrations of, for example, 10 mM can very conveniently be measured in a couple of hours—such samples the Mossbauer spectroscopists like the most. In any case, for... 

The proton NMR spectrum of the Me2S0 extract of the lignite was obtained using a XL-200 Fourier transform proton NMR spectrometer. Details of lignite extraction with Me2S0 are described elsewhere (, 5). Instrumental conditions for the measurement of the spectrum were as follows frequency - 200 MHz proton sample state - liquid solution solvent - Me2S0-dg locked sample concentration - ca. 200 mg/10 ml probe temperature - 25 C sweep width - 2600.1 Hz acquisition time - 1 second internal reference - tetramethyl silane number of transients - 1500 pulse width - 5.0 piseconds. 

Figure 5 shows the absorption spectrum of irradiated SAA and the emission spectrum of irradiated SAT. As can be seen, the spectra are red-shifted compared to the corresponding spectra of the cis-quinoid tautomers by about 2000 cm . The transient observed after flashing a liquid solution shows a spectrum similar, although structureless, to the photoproduct in solid solution (Fig. 6). 

In liquid solution, it has been shown by Wettermark and Dogllottl (55) that a transient showing a similar absorption spectrum (Fig. 5) as the trans-qulnone Is formed, which decays In the millisecond range. 

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