Spectra of gases

Titanium Diffuoride. Unlike other titanium dihalides, titanium difluoride [13814-20-5] is known only from mass spectra of gases. 

Nikitin E. E. On the interpretation of pressure induced infrared spectra of gases. Opt. Spectr. 8, 135-6 (I960) [Optika i Spectr. 8, 264-6 (I960)]. 

Although Hq. (152) can in principle be solved by the development of y(x) in a power series, the periodicity of the argument of cosine, namely, 2jc = Na complicates the problem. The most important application of Mathieu s equation to internal rotation in molecules is in the analysis of the microwave spectra of gases and vapors. The needed solutions to equations such as Eq. (152) are usually obtained numerically. 

For measuring infrared absorption spectra of gases adsorbed on the surfaces of metal single crystals or polycrystalline foils, one uses reflection absorption infrared... 

Solid samples or solid extracts can be mixed and ground with potassium bromide (KBr),pressed to form a transparent pellet, and a spectrum obtained from the pellet (see C in Figure 14.3). There are gas cells for obtaining spectra of gases and many other methods for obtaining spectra from liquid and solid samples that are not as frequently used as these [13-17],... 

On Bjerrum, see Assmus, "Molecular Structure," 5465, 6873 and Assmus, "The Molecular Tradition," esp. 217231. Niels Bjerrum, "On the Infrared Spectra of Gases. III. The Configuration of the Carbon Dioxide Molecule and the Laws of Intramolecular Forces" (1914), 4255, in N. Bjerrum, Selected Papers (Copenhagen ... 

With single-mode lasers the resolution can be considerably improved since the laser line width is then reduced below lO cm". Rotational Raman spectra of gases could be resolved using a multiple-pass Raman cell and a single-mode argon laser I85a) development of tunable... 

FIGURE 6.41 Infrared spectra of gases from burning a hardwood (a) when glowing combustion and white smoke are observed and (b) 1 min later when there is no longer white smoke (adapted from Yokelson et al., 1997). 

Most peaklike functions become more gaussianlike when convolved with one another. One notable exception of interest to spectroscopists is the Cauchy function, which is the familiar Lorentzian shape assumed by lines in the spectra of gases subject to pressure broadening ... 

Restricting ourselves to the optical spectra of gases, we now describe phenomena that cause a spectral line to have an inherent breadth. Even observations by a perfectly resolving spectrometer would show this broadening. Can the broadening be removed And if so, under what circumstances To answer these questions, we must first discuss the nature of the broadening. 

Infrared spectra may be obtained for gases, liquids, or solids. The spectra of gases or low-boiling liquids may be obtained by expansion of the sample into an evacuated cell. Gas cells are available in lengths of a few centimeters to 40 m. The sampling area of a standard IR spectrophotometer will not accommodate cells much longer than 10 cm long paths are achieved by multiple reflection optics. 

An understanding of the electronic structure of atoms is necessary for the study of the electronic structure of molecules and the nature of the chemical bond. Our knowledge of the electronic structure of atoms has been obtained almost entirely from the analysis of the spectra of gases. In this chapter we shall discuss the nature of spectra and the information about the electronic structure of atoms that has been derived from this information, in preparation for the later chapters of the book. The chapter ends with the statement of the formal rules for the formation of covalent bonds. 

The study of the absorption and emission spectra of gases confirms, and in some respects extends, the information about molecular motions provided by the considera-... 

Because of the failure of the attempts to observe an emission spectrum of chemisorbed CO, there is some doubt as to the scope of application of this method. The method is worthy of considerable attention because it provides a means of obtaining spectra of gases adsorbed on wires. The best chance for successful application lies in systems that can be heated to high (400° C.) temperatures without desorbing the chemisorbed gas. 

Another recent report by the same group [42] addressed the shape and intensity of SFG peaks in the spectra of gases on supported particles. As mentioned above, the spectra are affected by non-resonant absorption in the metal, although a detailed discussion of this finding is beyond the scope of this text. Finally, a promising new development is that the SFG technique has also been shown to... 

An alternate explanation for the 2100 cm.-1 band and its temperature variation is that it represents a transition from a thermally excited state. While hot bands are well documented in the infrared spectra of gases, they have been recognized only recently in solution spectra (Kraihanzel and West, 1962). A number of bands below 500 cm.-1 in the Raman spectrum of (CH3)3SiCN (Goubeau and Reyhing, 1958) could correspond to the thermally excited state and explain the observed intensity variation. In view of this alternate spectral interpretation and the equivocal nature of chemical evidence, the existence of trialkylsilyl isocyanides is questionable. 

Both phosgene and carbon monoxide were identified in IR spectra of gases generated from an equimolar mixture of oxalyl chloride and aluminum chloride at room temperature. 

Arthur Schuster, On Harmonic Ratios in the Spectra of Gases, Proceedings of the Royal Society 31, 337-347 (1881). 

Reproducible infrared techniques for recording spectra of gases chemisorbed on metals were first developed for samples consisting of small (<10(X8) particles of metal dispersed on silica (2). This method was applied to a study of carbon monoxide chemisorbed on copper, platinum, nickel and palladium. 

In the gaseous state coupling of the vibrational transitions with the rotational degrees of freedom give rise to rotational-vibrational bands (Fig. 2.6-1 A). The structures of these bands characterize the shape of a molecule and its symmetry (see Sec. 2.7). Spectral lines in the far-infrared range and in low-frequency Raman spectra are due to pure, quantized rotations of the molecules. Infrared and Raman spectra of gases are discussed in detail in Secs. 4.3.1 and 4.3.2. 

One of the main advantages of CARS and also of other nonlinear Raman spectroscopies is the high resolution that can be achieved in spectra of gases at low pressures. The reason for this is that the instrumental resolving power in these techniques depends only on the convoluted linewidths of the lasers used for excitation, whereas in linear Raman spectroscopy the resolution is determined by the monochromators used to disperse the observed scattered Raman light. 

The depolarization ratio of a band is very helpful in assigning vibrations in the Raman spectra of gases and liquids (Sec. 2.7.3.4). Vibrations of a totally symmetric representation can thus be distinguished from those associated with lower symmetry The breathing mode of the tetrahedral SiCU molecule at 424 cm , for instance, is the strongest band in one Raman spectrum but unobserved in another, depending upon the directions of the polarized radiation for excitation and observation. 

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