Absorption relative positions

The aggregation-induced changes of absorption spectra result from intermolecular interactions between closely spaced carotenoid molecules. For two molecules whose transition dipole moment vectors, p, are located at places characterized by position vectors /- and r2, with the relative position vector defined as R=r1-r2, Figure 8.3, the interaction energy is expressed as (van Amerongen et al. 2000)... 

Note In describing the shifts of absorption peaks or their relative positions, we have... 

A fluorophore in the proximity of the NP senses the altered EM-field and its fluorescence properties are consequently modified. There are (at least) two enhancement effects an increase in the excitation of the fluorophore and an increase in its quantum efficiency (QE). The increased excitation of the fluorophore is directly proportional to the to the square of the strength of the E-field and is a function of the wavelength and relative position of the NP. The maximum enhancement of this type is achieved if /.res equals the peak absorption wavelength of the dye. 

It is important to note that the stiffer the bond or the lighter the atoms, the higher is the wavenumber of the fundamental and vice versa. Qualitative conclusions can therefore be reached from the relative positions of absorption bands in the infrared region (vide infra). 

The F center absorption maximum for KC1 is at 565 nm and that for KF is 460 nm (Table 9.1). (a) What is the composition of a natural crystal with color centers showing an absorption peak at 500 nm (b) If the absorption peak for KF corresponds to the promotion of an electron from the F center to the conduction band, determine the energy of the color center with respect to the conduction band. (The band gap in KF is 10.7 eV.) If the relative position of the color center energy level remains the same throughout the KF-KC1 solid solution range, estimate (c) the band gap of KC1 and (d) the band gap for the natural crystal. 

Fig. 3.1. Perrin-Jablonski diagram and illustration of the relative positions of absorption, fluorescence and phosphorescence spectra.

Free primary amino acids are characterized by the following absorptions (most of the work was done with a-amino acids, but the relative positions of the amino and carboxyl groups seem to have little effect) ... 

In setting out to discover the relative positions of the atoms in a crystal, it is best, when the unit cell dimensions have been determined and the intensities of the reflections measured, to calculate F for each reflection. (See Chapter VII.) Absolute values of F, derived from intensities in relation to that of the primary beam, form the ideal experimental materisi, though very many structures have been determined from a set of relative F s. The reliability of the set-of figures depends on the success with which the corrections for thermal vibrations, absorption, and extinction effects have been estimated. 

The excited state lifetimes and luminescence properties of metal complexes are related to the relative positions of the potential energy wells shown in Figure 4.77. On the left we have a lowest excited state which resembles geometrically the ground state (the internuclear distances, r, are similar). The crossing between these states requires a high activation barrier E (in a classical picture) and the excited state lifetime is therefore relatively long. The Stoke s shift between the absorption band (a) and the emission band (e)... 

FIGURE 7. Relative positions of absorption, fluorescence, and phosphorescence The 0-0 peak is common to both absorption and fluorescence spectra (see Fig. 6). ISC, Intersystem crossing. (Modified from Ref. 2.)... 

The threshold energy needed for light absorption (i.e., the band-gap energy) and the relative positions of the band edges i.e., the flat band potential) are intrinsic material properties of each semiconductor. 

The profile of the absorption spectrum depends extensively on the relative position of the fy value, which depends on the different vibrational states. The intensity of the absorption spectrum depends, among others, on the population of molecules reaching the excited state. The more important is this population, the higher the intensity of the corresponding absorption spectrum will be. Therefore, recording absorption spectrum of the same molecule at different temperatures should yield, in principle, an altered or modified absorption spectrum. 

Solids give rise to the "wide-line" or (broad-line) spectra, because the local fields arising from nuclear magnetic dipole interactions contribute significantly to the total field experienced by a nucleus in the solid state. A measure of this direct spin-spin interaction is the spin-spin relaxation time T2 (see Sect. 12.2.1.3), which is much shorter in solids than in liquids, and thus gives rise to broader lines (of the order of 10-6 to 10 4 T, depending on the kind of nucleus). Now the contour of the absorption line provides information as to the relative position of the neighbouring nuclei. 

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