Spectra of liquids

Fig. 14-17. Infrared absorption spectra of liquid carbon tetrachloride, CCU, carbon disulfide, CSt, and a mixture of the two.

Although long-time Debye relaxation proceeds exponentially, short-time deviations are detectable which represent inertial effects (free rotation between collisions) as well as interparticle interaction during collisions. In Debye s limit the spectra have already collapsed and their Lorentzian centre has a width proportional to the rotational diffusion coefficient. In fact this result is model-independent. Only shape analysis of the far wings can discriminate between different models of molecular reorientation and explain the high-frequency pecularities of IR and FIR spectra (like Poley absorption). In the conclusion of Chapter 2 we attract the readers attention to the solution of the inverse problem which is the extraction of the angular momentum correlation function from optical spectra of liquids. 

Of course, knowledge of the entire spectrum does provide more information. If the shape of the wings of G (co) is established correctly, then not only the value of tj but also angular momentum correlation function Kj(t) may be determined. Thus, in order to obtain full information from the optical spectra of liquids, it is necessary to use their periphery as well as the central Lorentzian part of the spectrum. In terms of correlation functions this means that the initial non-exponential relaxation, which characterizes the system s behaviour during free rotation, is of no less importance than its long-time exponential behaviour. Therefore, we pay special attention to how dynamic effects may be taken into account in the theory of orientational relaxation. 

Lynden-Bell R. M. The effect of molecular reorientation on the line-shapes of degenerate vibrations in infra-red and Raman spectra of liquids, Mol. Phys. 31, 1653-62 (1976). 

Abstract Molecular spectroscopy is one of the most important means to characterize the various species in solid, hquid and gaseous elemental sulfur. In this chapter the vibrational, UV-Vis and mass spectra of sulfur molecules with between 2 and 20 atoms are critically reviewed together with the spectra of liquid sulfur and of solid allotropes including polymeric and high-pressure phases. In particular, low temperature Raman spectroscopy is a suitable technique to identify single species in mixtures. In mass spectra cluster cations with up to 56 atoms have been observed but fragmentation processes cause serious difficulties. The UV-Vis spectra of S4 are reassigned. The modern XANES spectroscopy has just started to be applied to sulfur allotropes and other sulfur compounds. 

Unlike high-resolution NMR spectra of bulk solutions where NMR linewidths well below 1 Hz can be obtained routinely, NMR spectra of liquids permeating porous solids in most cases will not exhibit such a high spectral resolution. First of all, the interaction of liquid phase molecules with pore walls of the catalyst and rapid diffusion-driven intrapore transport will lead to a pronounced homogeneous broadening of the observed NMR lines. Smaller pore sizes and the presence of paramagnetic impurities in the solid material usually aggravate the situation and thus should be avoided. Another reason why NMR spectra of liquids in porous... 

The Raman, mid- and far-IR spectra of liquid and solid CH3GeD2NCO and CD3GeH2NCO were assigned and applied for the conformational analysis of these isocyanates553. 

First let us see how the absorption spectra of liquids is recorded in a spectrophotometer. 

With the Structural information obtained from the crystals, we are now in a position to discuss the liquid structure of bmimX ionic liquids. Raman spectra of liquid bmimX (X = Cl, Br, 1, BF4, PFg) are shown in Fig. 10. The Raman spectra of bmimCl Crystal (1) and bmimBr are also shown as references. All Raman spectra were measured at room temperature. The Raman spectra of liquid bmimCl and bmimBr were obtained from their supercooled states. 

The Raman spectra of the BF4 and PFg anions are already well known. Except for these anion bands that are deleted in Fig. 10, the Raman spectra of liquid bmimX are surprisingly alike with one another. It seems that the stmcture of the bmim+ cation is very similar in these liquids. Both of the two sets of key bands, the 625-cm and 730-cm bands for the trans conformation and the 603-cm and 701-cm bands for the gauche conformation, appear in all of the... 

Figure 10. Raman spectra of liquid bmimX, where X = Cl (a), Br ( ), I (c), [BF4] (d), and [PF6] (d). The anion bands in (d) and (e) are deleted. Raman spectra of bmimCl Crystal (1) and that of crystalline bmimBr are also shown as references in (/) and (g), respectively.

The spectra of methane, adsorbed at 90° K., showed a weak band at 2,899 cm.", in addition to a strong band (vt) at 3,006 cm. h This weak band was assigned to the I l symmetrical breathing frequency of methane, which is normally observed only in the bulk state in the Raman spectrum at 2,916 cm. h No over-all dipole change is associated with the vi vibration consequently, it is forbidden in the infrared spectra of liquid and gaseous methane. The appearance of this band is a direct measure of the... 

Sharp absorption bands are typically not observed in UV and visible absorption spectra of liquid samples. This is the consequence of the presence of the vibrational and rotational fine structure that become superimposed on the potential energy surfaces of the electronic transitions. Fine structure in UV/vis absorption spectra can be detected for samples in vapor phase or in nonpolar solvents. 

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. 

A complete analysis of the IR spectra of thienothiophenes 1 and 2 in the gaseous, liquid, and crystalline states was carried out by Kimel feld et a/. The following isotopically substituted compounds were also studied 2-deuterothieno[2,3-h]thiophene (l-2d), 2-deuterothieno[3,2-I)]-thiophene (2-2d), 2,5-dideuterothieno[2,3-h]thiophene (l-2,5-d2), and 2,5-dideuterothieno[3,2-h]thiophene (2-2,5-dj). The IR spectra of oriented polycrystalline films of all compounds were measured in polarized light, and Raman spectra of liquid thienothiophenes 1, l-2d, and 1-2,5-dj, of crystals of thienothiophenes 2 and 2-2,5-d2 and melts of thienothiophenes 2 and 2-2d were analyzed. The planar structure of point-group Cj, for thienothiophene 1 in the liquid and gaseous states was assumed. Then the thirty vibrations of compounds 1 and l-2,5-d2 can be divided into four symmetry classes Aj (11), Bj (10), A2 (4), and B2 (5) the vibrations of molecule (l-2d) (C, symmetry) are divided into two classes A (21) and A" (9). 

Fig. 3 IPA (dashed line) and 2PA (solid line) spectra of liquid benzene. The 2PA spectrum was obtained by the thermal lensing method. The units on the energy scale are kilokaysers (1 kK = 1000 cm ) and refer to the total energy of the transition. 0-0 is the origin of the Lb band, 18, 14, and 1 are indices for the vibrational modes (the superscript and subscript are the quantum numbers for the mode in the excited state and ground state, respectively). Reproduced with permission from [33]. 1986, American Chemical Society...

It is common, however, for liquid-phase systems to include many specific absorbing species. Such species could include isotopic variations, conformational isomers, and solvent-solute interactions resulting in varied-lifetime transient associations between molecules. Distributions resulting from these effects give the Voigt profile utility in studying liquid spectra. We must understand, however, that the functions introduced here are only rough approximations when applied to the spectra of liquids because of the complexities just mentioned and others beyond the scope of this work. 

The Raman spectra of liquid B203 have been examined by Young and Westerdahl (62) up to 800°C. The intensity of the 808 cm-1 line was found to decrease rapidly with increasing temperature. These authors have also concluded that a major structural change has occurred in the network-like melt which is compatible with a model postulated by the present author (SO). 

The infrared reflection spectra of liquid Si02 has also been studied up to 2000°C (4%)- The room temperature 1120 cm 1 band of vitreous Si02 was found to have shifted to 1054 cm 1 at 2000°C and with greatly reduced intensity. No direct interpretation was made. 

Fig. 19.—Ultravoilet Absorption Spectra of Liquid Bromine and Iodine.

Low frequency spectra of liquids are notably deficient of any structure, and it has long been hoped that a technique would be discovered that provides the same type of line narrowing enjoyed in echo-based electronic and NMR spectroscopy. Tanimura and Mukamel observed that such a technique was possible, and proposed a two-time interval, fifth-order Raman pulse sequence capable of distinguishing, for example, inhomogeneous and homogeneous contributions to the lineshape.[4] The pulse sequence, shown in Fig. 1, is simply an extension of conventional time-domain third-order Raman-based methods. At the... 

Many-body effects are evident in the induced spectra of liquids and solids these spectra may bear a superficial resemblence to the binary spectra, but significant quantitative differences exist which distinguish the various many-body spectra from the binary ones. 

The spectra of liquids and solids are known to have strong induced components. Liquids and solids are, however, so dense that many-body terms dominate the spectra the binary and ternary spectral components which are the main topic of this work (and which are usually measurable in compressed gases at densities much lower than liquid state) will often resemble the spectra of liquids and solids, but a critical comparison will reveal important qualitative and quantitative differences. Nevertheless, a study of binary spectra will help to illuminate important aspects of the theoretical descriptions of liquid spectra and may be considered a basic input into the theory of liquid interactions with radiation. 

The spectra of liquids and solids cannot be studied here in any detail we refer the reader to other works, such as the two volumes by Gray and Gubbins, and the review articles by Guillot and Birnbaum (1989). 

U. Buontempo, S. Cunsolo, and P. Dore. Intercollisional memory effects and short-time behavior of the velocity-autocorrelation function from translational spectra of liquid mixtures. Phys. Rev., A 10 913, 1974. 

An important difference between atomic and molecular spectroscopy is the width of absorption or emission bands. Spectra of liquids and solids typically have bandwidths of — 100 nm, as in Figures 18-7 and 18-14. In contrast, spectra of gaseous atoms consist of sharp lines with widths of —0.001 nm (Figure 21-3). Lines are so sharp that there is usu-... 

In addition to frequency shifts, new vibrational bands occasionally appear in the liquid state as compared to the gas phase. An example is formic acid, HCOOH. At high temperatures, the vapor shows a characteristic O—H stretching vibrational band at 3750 cm-1 as the temperature of the gas is lowered, this band disappears and a new band at 3080 cm -1 appears. In the liquid state, only the 3080 cm"1 band is evident. The new band is due to O—H vibration in the hydrogen-bonded dimer. Hydrogen bonding also affects the IR spectra of liquid CH3OH and H20. 

This term is called the Fermi contact term. That part of the electron-nucleus magnetic-dipole interaction represented by (8.104) depends on the angular coordinates of the electron and is therefore anisotropic in contrast, the Fermi contact energy (8.108) is isotropic. The contact term plays an important role in the electron-coupled nuclear spin-spin interactions seen in the NMR spectra of liquids. 

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