Benzene vibrational spectrum

B.S. Hudson, D.A. Braden, D.G. Allis, T. Jenkins, S. Baronov, C. Middleton, R. Withnall C.M. Brown (2004). J. Phys. Chem. A, 108, 7356-7363. The crystalline enol of 1,3-cyclohexanedione and its complex with benzene vibrational spectra, simulation of structure and dynamics and evidence for cooperative hydrogen bonding. 

Figure 17 Raman spectrum of liquid benzene with CC1. The CCI4 has little effect on the benzene vibrational spectrum or the benzene VER rates. Monitoring the CCI4 vibrational transitions while pumping benzene vibrations provides an indication of the energy build up in the bath. (From Ref. 49.)... 

The vibrational spectrum of benzene around 1000 cnf has also been measured. IQ. Benzene was physisorbed on a cooled copper substrate in the vacuum chamber. Figure 19 shows the transmission for several thicknesses of benzene and a prism separation of 3 cm. The thickness was determined from the measured transmission in transparent regions using Eg. (7). The solid curves were calculated from Eqs. (5) and (6) using optical constants for benzene obtained from an ordinary transmission experiment.il The benzene film was assumed to be isotropic. Of the two absorption lines seen, one belongs to an in-plane vibrational mode, and one to an out-of-plane vibration. Since the electric field of the SEW is primarily perpendicular to the surface, the benzene molecules are clearly not all parallel or all perpendicular to the copper surface. Also it should be noted that the frequencies are the same (within the experimental resolution) as those of solid benzene22 and of nearly the same width. These features indicate that the benzene interacts only weakly with the copper surface, as would be expected for physisorbed molecules. 

Vibrational analysis of the benzene phosphorescence bands indicates that the radiative activity is induced predominantly by e2g vibrations [155, 156]. A weak but observable activity of b2g vibrations has also been found [156, 155, 157]. By introducing spin-orbit- and vibronic coupling through second order perturbation theory Albrecht [158] showed that the vibronic interaction within the triplet manifold is responsible for the larger part of the phosphorescence intensity. This also follows from comparison of the vibrational structure in phosphorescence and fluorescence spectra [159]. The benzene phosphorescence spectrum in rigid glasses [155] reveals a dominant vibronic activity of... 

Obviously, only molecules with partially filled orbitals display Jahn-Teller distortion. As was shown in Section 6.3.2, the electronic ground state of molecules with completely filled orbitals is always totally symmetric, and thus cannot be degenerate. In comparison with the above-mentioned unstable H3 molecule, Hj" has only two electrons in an a symmetry orbital therefore, its electronic ground state is totally symmetric, and the D3/,-symmetry triangular structure of this ion is stable (see, e.g., Reference [62]). On the other hand, take the benzene molecule, e.g., whose ground electronic state is of Alg symmetry and the molecule is stable and its structure is well understood. At the same time, in its cation, C6Hg, it loses one electron from an c -symmetry doubly-degenerate orbital, so that orbital is left with only one electron. The electronic state of the cation has E g symmetry and thus, it is subject to Jahn-Teller effect. Indeed, its vibrational spectrum is extremely complicated and can only be satisfactory explained if the Jahn-Teller distortion is taken into consideration (see, e.g., Reference [63]). 

The NH-tt type hydrogen bond between the charged aniline and neutral benzene is deduced by the vibrational spectrum of the [aniline/benzene]4 complex. By using a time-of-flight mass spectrometer with an ion reflector, the intermolecular interactions in aniline/benzene trimer ions were investigated. The NH-7T and N—H N structures of the [aniline/benzene]+ trimer ions based on theoretical calculations are reported in Scheme 19183. 

The CNM analysis in terms of adiabatic internal modes has been carried out to correlate the calculated vibrational spectra of the three dehydrobenzenes, namely ortho- (3), meta- (4) and para-henzyne (5), with the vibrational spectrum of benzene (6). Investigation of dehydrobenzenes with the help of infrared spectroscopy is of considerable interest at the moment since these molecules have been found to represent important intermediates in the reaction of enediyne anticancer drugs with DNA molecules [34-37]. Both 4 and 5 are singlet biradicals and, therefore, they are so labile that they can only be trapped at low temperatures in an argon matrix upon photolytic decomposition of a suitable precursor [38-40]. 

Figure 6.7. Structure and vibrational spectrum of benzene on surfaces and in organometallic clusters [25],... 

Indium(III) iodide is a yellow hygroscopic crystalline solid, mp 210°. The compound exists in the solid state as iodine bridged dimers (I2lnl2lnl2) and is readily soluble in organic solvents such as benzene, chloroform, and diethyl ether. The vibrational spectrum has been reported, but the observed infrared and Raman frequencies occur in the far-infrared region, below 250 cm . ... 

Fig. 21. The vibrational spectrum of K (C6H6)3-5(H20)i. Bach additional benzene significantly alters the environment of the water molecule as shown to the right of the spectra.

A scaled AM 1 field has been used successfully to help identify the fundamental vibrational bands of indole <88JCP(88)7295>. Pyrrole and benzene were used to generate a set of scale factors which were then used to simulate a complete vibrational spectrum (included in Table 40, see Section 2.01.3.5) which in turn was used to identify the fundamental vibrations of indole, and to calculate the derived force constants. 

In this chapter a detailed analysis of the vibrational spectrum of the benzene molecule will be carried out in order to illustrate in a coordinated form the material from several previous chapters, in particular, Chap. 4 through 9. Several representative references to original papers on this subject are given in the footnote. ... 

The structure for benzene which rvill be assumed in this chapter is one in which all atoms are coplanar with the carbon atoms and the hydrogen atoms at the corners of concentric, regular hexagons (Fig. 10-1). The Kekul6 structure, in which alternate carbon-carbon bonds, but not adjacent ones, are equivalent, would be somewhat less symmetrical, but modern theories of valence regard all six such bonds as equivalent. Moreover, there is good experimental evidence (aside from the vibrational spectrum) for the most symmetrical planar structure for example, it is supported by electron diffraction experiments. ... 

The first overtone doublet near 6000 cm (1670 nm) is actually composed primarily of IR-inactive C-H-stretching vibrations. As described in Table 4.1 and Figure 4.1, both of the bands near 6000 cm are composed of a Raman active vibration and a vibration that is neither IR nor Raman active. The benzene NIR spectrum is shown in Figure 4.2. 

Figure 13 Rotation-vibration spectrum of benzene CeHg (a) infrared spectrum in absorbance units (b) Raman spectrum, compiled from several spectra recorded under different conditions, but plotted on an approximately equivalent intensity scale. The peaks of and V2 are off scale (pressure, 13 kPa laser power, 6-10 W at 514.5 nm spectral slit width, 2 cm" ). (From Ref. 43, with permission.)... 

The absorption with the maximum at ca 80cm in the PS spectrum is mainly due to benzene ring librations [75]. A similar band at 75cm is observed in the spectrum of liquid benzene [76] and the absorption with a maximum at 60cm in the Raman spectrum of PS is assigned to this mechanism [36], Lattice vibration spectrum of crystalline benzene in the frequency range under discussion exhibits bands at 65, 74, 92 and 116 cm ... 

Figure 5 A CARS vibrational spectrum produced by monitoring the output beam intensity (at C04) while wavelength scanning an OPO (see Figure 4(B)). This spectrum shows Raman-active peaks from benzene (b), oxygen (0), nitrogen (n), and cyclohexane (c) covering a range from 681 cm- (Aqpo = 552 nm) to 3098 cm- (Iqpo = 637 nm). Zero frequency shift corresponds tolopo = 532 nm.

The vibrational spectrum of benzene has been discussed many times (29, 102-108) and, except for the frequencies of representation J52 , has been assigned unequivocally (109,110). Interestingly the symmetry D was not immediately established from the vibrational spectrum, since the latter exhibits some pecularities, such as Fermi resonance of combination bands, etc. This was not at first recognized. From the spectral predictions of Table XXVIII we now know that four infrared- and seven Raman-active n.v. should be observed for the planar De molecule. 

The changes in the vibrational spectrum of iodine cyanide, iodine monochloride and diiodine as these molecules form halogen-bonded complexes B- ICN, B- -ICl and B- I2 with series of Lewis bases B have been extensively studied [35, 36, 273-277]. The main perturbation is a lowering of the frequency of the I—CN, I—Cl and I—I stretching motions. These frequency shifts are greater for strong bases, such as pyridines, than for weak bases, such as benzene or dioxane. Hence correlations were attempted between frequency shifts... 

Figure Bl.6.10 Energy-loss spectrum of 3.5 eV electrons specularly reflected from benzene absorbed on the rheniiun(l 11) surface [H]. Excitation of C-H vibrational modes appears at 100, 140 and 372 meV. Only modes with a changing electric dipole perpendicular to the surface are allowed for excitation in specular reflection. The great intensity of the out-of-plane C-H bending mode at 100 meV confimis that the plane of the molecule is parallel to the metal surface. Transitions at 43, 68 and 176 meV are associated with Rli-C and C-C vibrations.

Carbon-hydrogen stretching vibrations with frequencies above 3000 cm are also found m arenes such as tert butylbenzene as shown m Figure 13 33 This spectrum also contains two intense bands at 760 and 700 cm which are characteristic of monosub stituted benzene rings Other substitution patterns some of which are listed m Table 13 4 give different combinations of peaks... 

Nevertheless, 1,4-difluorobenzene has a rich two-photon fluorescence excitation spectrum, shown in Figure 9.29. The position of the forbidden Og (labelled 0-0) band is shown. All the vibronic transitions observed in the band system are induced by non-totally symmetric vibrations, rather like the one-photon case of benzene discussed in Section 7.3.4.2(b). The two-photon transition moment may become non-zero when certain vibrations are excited. 

It is possible that the complexes benzene- -HX can be described in a similar way, but in the absence of any observed non-rigid-rotor behaviour or a vibrational satellite spectrum, it is not possible to distinguish between a strictly C6v equilibrium geometry and one of the type observed for benzene- ClF. In either case, the vibrational wavefunctions will have C6v symmetry, however. 

---