Splitting Davydov

Optical misalignment of the sample. The energy difference between the two Davydov components leads to a measured Davydov splitting of 2600 cm .  

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The resonance splitting of intramolecular modes in the crystalline state is often called Davydov splitting or factor group splitting . In contrast to the static field effects of the crystal, this splitting is due to the dynamical interaction of the constituents in the primitive cell... 

Chapter 3 is devoted to dipole dispersion laws for collective excitations on various planar lattices. For several orientationally inequivalent molecules in the unit cell of a two-dimensional lattice, a corresponding number of colective excitation bands arise and hence Davydov-split spectral lines are observed. Constructing the theory for these phenomena, we exemplify it by simple chain-like orientational structures on planar lattices and by the system CO2/NaCl(100). The latter is characterized by Davydov-split asymmetric stretching vibrations and two bending modes. An analytical theoretical analysis of vibrational frequencies and integrated absorptions for six spectral lines observed in the spectrum of this system provides an excellent agreement between calculated and measured data. 

Projections of molecular axes onto the surface plane form chain-like structures in which the chains with identically oriented molecules alternate (with the exception of oxygen molecules). The Davydov splitting of spectral lines represents the main spectroscopic manifestation of adsorbed structures with several orientationally inequivalent molecules in the unit cell of a two-dimensional adsorbate lattice. Many... 

The v2 bending vibration is a quartet or, in a simplified picture, two Davydov doublets as a consequence of a site-symmetry-induced doublet (see Fig. 2.6).40 A system of particular interest is CO/NaCl(100) it is characterized by inclined molecular orientations with =25° and antiferroelectric ordering of chains at low temperatures (see Fig. 2.7) which is removed on the phase transition at T 25 K. This structural information is deduced from the observed Davydov splitting of the spectral line for the CO stretching vibrations at 2155 cm 1 and T<24 K (see Fig. 

Complex orientational structures and corresponding Davydov-split spectral lines... 

Taking into consideration relations (3.2.4), expressions (3.2.6) for absorption lines allowed in infrared spectra (A/ 0) are the same as those obtained formerly by an alternative method which involves no sublattice concept.81 The determination of Davydov splittings as squared frequency differences (3.2.6) results in their independence from the static frequency renormalization. For structures with [Pg.62]

Here the indices X, V, Z indicate vibration polarizations, other designations being the same as in expressions (3.2.6). Finally, the Davydov splitting of spectral lines obtained as... 

As seen from Chapter 2, adsorbed molecules often form monolayers with chain orientational structures in which the chains with identically oriented molecules alternate (Fig. 2.4). Consider the Davydov splitting of vibrational spectral lines in such systems. Let molecular orientations be specified by the angles 6> and spherical coordinate system with the z-axis perpendicular to the lattice plane ... 

Now we pass on the analysis of the relations derived focusing on several particular cases of importance which enable us of correlating the calculated values with the available experimental data. CO molecules adsorbed on the (100) face of a NaCl crystal reside at the sites of a square lattice (a = b/2 = 3.988 A) at sufficiently low temperatures (T < 25 K), they have inclined orientations (B = 25°) with alternating dipole moment projections onto the axes of the neighboring chains (

x = 180°).28 For this system, the Davydov splitting of vibration spectral lines is determined as ... 

We now turn to a more complex instance of the Davydov-split spectral lines corresponding to the bending vibrations of C02 molecules in a monolayer adsorbed on the NaCl(100) surface. A molecule C02 in gaseous phase exhibits two degenerate bending vibrations in the plane perpendicular to the long molecular axis. 

Fig. 4.8. Temperature dependences of shifts (a) and widths (b) for Davydov-split spectral lines of local vibrations in the 2x1 phase of CO molecules adsorbed on the NaCI(lOO) surface.

Table 4.3. Parameters of Davydov-split spectral lines for the 2x1 phase of the system CO/NaCl(l 00) calculated by the formulae of Erley and Persson (4.3.49) and by the generalized formula (4.3.47) accounting for the dispersion of low-fiequency CO vibrations.

Losytskyy MYu, Yashchuk VM, Lukashov SS, Yarmoluk SM (2002) Davydov splitting in spectra of cyanine dye J-aggregates, formed on the polynucleotide. J Fluoresc 12 109-112... 

The effect of intermolecular interactions can be readily observed when comparing the absorption spectrum of a molecule in solution to that in the solid state. In solution, where the molecules can be considered as isolated, the spectra are characterized by sharp lines corresponding to absorption bands. However, in the solid, intermolecular interactions cause the formation of exciton bands and splitting of the levels. This phenomenon is often referred to as Davydov splitting. This splitting is thus a measure of the strength of the interactions and for MOMs it can amount to 0.2-0.3 eV. 

Q. Williams, E. Knittle, Infrared and Raman spectra of fluorapatite at high pressures Compression-induced changes in phosphate site and Davydov splittings, J. Phys. Chem. Sol. 57 (1996) 417-422. 

Interaction of two chromophores exhibiting allowed (strong) n-n absorption bands splits the excited state into two energy levels with the energy gap 2VSj (Davydov splitting), Figure 12. 

Figure 13. Definition of exciton chirality. Summation of the two Cotton effects (broken lines) separated by Davydov splitting A). gives the curves shown in solid lines. Adapted from N. Harada, K. Nakanishi. Circular Dichroic Spectroscopy - Exciton Coupling in Organic Stereochemistry, University Science Books. Mill Valley, California. 1983...

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