Carbon tetrachloride, Raman spectra

Solutions of dinitrogen pentoxide in nitric acid or sulphuric acid exhibit absorptions in the Raman spectrum at 1050 and 1400 cm with intensities proportional to the stoichiometric concentration of dinitrogen pentoxide, showing that in these media the ionization of dinitrogen pentoxide is complete. Concentrated solutions in water (mole fraction of NgOg > 0-5) show some ionization to nitrate and nitronium ion. Dinitrogen pentoxide is not ionized in solutions in carbon tetrachloride, chloroform or nitromethane. ... 

Figure 7.2 Complete Raman spectrum of carbon tetrachloride, illustrating the Stokes Raman portion (on left, negative shifts), Rayleigh scattering (center, 0 shift), and the anti-Stokes Raman portion (on right, positive shifts). Reprinted from Nakamoto (1997) [7] and used by permission of John Wiley Sons, Ltd., Chichester, UK.

Fig. 1. Stokes and anti-Stokes Raman spectrum of carbon tetrachloride...

The absorption bands in the ultraviolet and visible part of the spectrum correspond to changes in the energy of the electrons but simultaneously in the vibrational and rotational energy of the molecule. In this way a system of bands is produced in the gaseous state. In the liquid state there is nothing of the rotational fine structure to be seen, and usually little or nothing of the vibrational structure, as a result of the interaction with the molecules of the solvent. With aromatic compounds in non-polar solvents such as hexane and carbon tetrachloride the vibrational structure is, however, still clearly visible in the ultraviolet absorption spectrum. This vibrational structure is mainly determined by the vibrations of the excited state, which therefore do not occur in the infrared and Raman spectrum of the normal molecule. 

The scattered radiation has a spectrum characteristic of the given substance, with an intense band at the incident frequency, vq, resulting from Rayleigh scattering, and fainter Raman bands on both sides of vo at distances corresponding to the molecular vibrational frequencies, v. Typical examples of such bands are seen in Figure 6, which displays the Raman spectra obtained on pure carbon tetrachloride, CCI4, at 298 K (hquid) and 77 K (frozen liquid) upon excitation with an Ar+ ion laser hue at 488.0 nm (20492 cm The measured... 

H. S. Gabelnick and H. L. Strauss. Low-frequency motions in liquid carbon-tetrachloride II. The Raman spectrum. J. Chem. Phys., 49 2334-2338 (1968). 

Quinet et al.,s4 in have interpreted their measurements of the hyper-Raman spectrum of carbon tetrachloride through ab initio TDHF simulations and find satisfactory agreement between theory and experiment. 

Fig. 5.12 Raman spectrum of carbon tetrachloride obtained using an argon-ion laser operating at 488.0 nm. Each line is labeled in terms of its shift from the central Rayleigh line. (From reference G5, with permission.)...

Structural features in unsaturated fatty acid methyl esters (in carbon tetrachloride solution) can give rise to distinctive bands in Raman spectroscopy [208-210]. For example, characteristic Raman bands are found for c s-double bonds (1656 cm ), frans-double bonds (1670 cm ) and triple bonds (2232 and 2291 cm ) a terminal triple bond gives a single band at 2120 cm (this group does not give a distinctive band in IR spectroscopy). Again, the position of a double bond does not affect the spectrum significantly unless it is at either extremity of the molecule. 

Instructional programs relying on home-built scanning monochromator systems and low-power lasers have usually been limited to simple demonstrations of spectra of neat liquids. Carbon tetrachloride has been a perennial favorite because the spectrum is strong and easily interpreted [7,10]. A comparison of the spectra of carbon tetrachloride, chloroform, and methylene chloride is also common, as is a comparison of the spectra of benzene and cyclohexane. Even with these systems, polarization effects can be demonstrated and selection rules taught. Details of the vibrational spectra, particularly chlorine isotope effects, may be difficult unless the instrument resolution is 5 cm or better. Because FTIR instruments are generally available, comparison of the Raman and infrared spectra of liquids is often stressed. 

Pn [Eq- (1.125)] will have a value between 0 and y and Pp [Eq. (1.126)] will have a value between 0 and For the special case of an isotropic molecule a is zero so p and Pp are both zero for totally symmetric vibrations. If the vibrationally-distorted molecule is less symmetrical than the molecule in the equilibrium configuration, then al = 0 and is j and pp is in the Raman spectrum. Therefore, a measurement of the depolarization ratio provides a means of distinguishing totally symmetrical vibrations from the rest. See Fig. 1.35 for a polarized Raman spectrum of chloroform, and Fig. 1.36 for a polarized Raman spectrum of carbon tetrachloride, which is an isotropic molecule. 

Figure 6.11 Raman spectrum of tetrachloromethane (carbon tetrachloride) taken using the blue line of a mercury arc lamp to give an exciting frequency of 22 938 cm The top scale shows the wavenumber of the radiation detected, the Rayliegh line is shown in the centre of the diagram and the bottom scale shows the relative frequency shift. Stokes lines occur at lower frequencies to the left of the Rayleigh line and anti-Stokes to the right (Used with permission from the Journal of Chemical Education 77 5 (1967). Copyright 2000, Division of Chemical Education, Inc.)...

Figure 7 Hyper-Raman spectra of CeHeexcited with a Nd YAG laser (Aq = 1.064 nm) Q-switched at 1 kHz (A) and of CgDe in the lower spectrum with the laser Q-switched at 6 kHz (B). Reproduced by permission of Elsevier Science from Acker WP, Leach DH and Chang RK (1989) Stokes and anti-Stokes hyper Raman scattering from benzene, deuterated benzene, and carbon tetrachloride. Chemical Physics Letters 155 491-495.

Figure 7 Mercury arc-excited Raman spectrum of carbon tetrachloride with photographic recording. (A) The spectrum of the mercury arc itself for reference. (B) The four Stokes lines (right side of the exciting line) and the weaker antiStokes (left side of the exciting line) lines, of which only three can be seen. From part of Plate 1, Raman CV and Krishnan KS (1929) The production of new radiations by light scattering. Proceedings of the Royal Society (London) A122 23-35. Reproduced from a photograph courtesy of Professor N. Sheppard, FRS, and with permission of the Royal Society.

Figure 8 Laser-excited Raman spectrum of carbon tetrachloride with photoelectric recording. Reproduced with the permission of Professor N. Sheppard, FRS.

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