Energy of electronic transitions

The ability to measure the energy of electronic transitions and their line widths accurately, in a convenient manner, is one of the most important aspects of semiconductor characterization. The former can be used to evaluate alloy compositions... 

The energy of electronic transitions corresponds to light in the visible, UV, and far-UV regions of the spectrum (Fig. 7.1). Absorption positions are normally expressed in wavelength units, usually nanometers (nm). If a compound absorbs in... 

UV-vis spectra of matrix-isolated intermediates are not so informative as matrix IR spectra. As a rule, an assignment of the UV spectrum to any intermediate follows after the identification of the latter by IR or esr spectroscopy. However, UV-vis spectra may sometimes be especially useful. It is well known, for example, that the energy of electronic transitions in singlet ground-state carbenes differs from that of the triplet species. In this way UV spectroscopy allows one to identify the ground state of the intermediate stabilized in the matrix in particular cases. This will be exemplified below. 

Finally we should mention the electrochromic shifts which are the changes in the energy of electronic transitions when an external electric field is applied to the sample. These effects are quite small but have proved useful for the measurements of the dipole moments and polarizabilities of excited molecules. 

The energy of electronic transition is equal to the energy difference between the starting energy level and the final level. Therefore, the transition energy E (J mol-1) is ... 

This equation has been used in several correlations of solvent effects on solute properties such as reaction rates and equilibrium constants of solvolyses, energy of electronic transitions, solvent-induced shifts in UV/visible, IR, and NMR spectroscopy, fluorescence lifetimes, and formation constants of hydrogen-bonded and Lewis acid/base complexes [Kamlet et al., 1986b]. 

Several solvent polarity scales were proposed to quantify the polar effects of solvents on physical properties and reactivity parameters in solution, such as rate of sol-volyses, energy of electronic transitions, and solvent-induced shifts in IR or NMR... 

Several solvent polarity scales vere proposed to quantify the polar effects of solvents on physical properties and reactivity parameters in solution, such as rate of solvolyses, energy of electronic transitions, solvent induced shifts in IR, or NMR spectroscopy. Most of the polarity scales vere derived by an empirical approach based on the principles of the linear free energies relationships applied to a chosen reference property and system vhere hydrogen bonding effects are assumed negligible [Reichardt,1965, 1990 Kamlet, Abboud et al., 1981, 1983]. 

The development of correlation schemes at the highest levels of theory (the CCSD(T) technique) allowed for very accurate DCB predictions of atomic properties for the heaviest elements up to Z=122 (see Chapter 2 in this book). Reliable electronic configurations were obtained assuring the position of the superheavy elements in the Periodic Table. Accurate ionization potentials, electron affinities and energies of electronic transitions (with the accuracy of below 0.01 eV) are presently available and can be used to assess the similarity between the heaviest elements and their lighter homologs in the Periodic Table. 

Since the extravalent d orbitals of sulfur, selenium, and tellurium are not occupied in the normal states of the free atom, their implicit functional form is determined by another criterion. The values of a number of molecular properties including ionization potentials, energies of electronic transitions, and overlap populations have been examined as a... 

The preceding section has shown that pressure leads to a small decrease in the Racah parameter B of transition metal systems. The small change in B indicates that pressure only weakly increases bonding covalency in transition metal systems. As a result, the energies of electronic transitions that depend primarily on covalency effects are expected to exhibit weak shifts to lower energy with pressure. 

Fig. 11. Effect of polar and non-polar solvents on the energies of electronic transitions of molecules in which the (n, ti ) and (tt, tz ) states are close together.

The energy of vibrational transitions is roughly one tenth of the energy of electronic transitions. Supposed that m) and n) in Fig. 1 are two quantum states of a given normal vibration in the ground electronic state and e) is an electronically excited state, IR... 

Analysis of products of decomposition Characteristic vibrational frequencies Characteristic vibrational frequencies Characteristic transition energies of any nucleus with a magnetic moment ( H, H, C, e, etc.) Characteristic energies of electronic transitions... 

In the molecule, the energy of a given state is determined not only by the distribution of the electrons but also by the particular state of the atomic nuclei building up the molecule. In addition to the energy of electron transition, there are energies involved in changing the states of oscillation and of rotation. This explains why the spectrum of a molecule consists of very many more lines than that of an atom. A mere glance shows that this is so, if one compares an atomic spectrum with a molecular spectrum the former can properly be described as a line spectrum, the latter as a band spectrum. 

Generally, INDO/S reproduces the energies of electronic transitions below 45,000 cm within 2,000 cm Charge transfer (CT) bands in non-solvatochromic systems and d-d... 

In addition, UV spectrum of the studied complexes was simulated by theoretical methods. The TD-DFT/B3PW91 approach was used to calculate the energies of electronic transitions in complexes VI and VII (Tables 10.7 and 10.8). 

The Z value was defined by Kosower as the energy of electronic transition corresponding to the charge-transfer absorption band of l-ethyl-4-carbo-methoxy pyridinium iodide, a substance which has an ultraviolet spectrum remarkably sensitive to solvent polarity. Application of this method involves the determination of the spectral characteristics of the solubilizate in a number of solvents of known Z values and the establishment of a relationship between Z values and the energy of transition which is readily obtained from the wavelength of maximum absorbance. From this relationship the Z value of the micellar micro-environment may be determined from the wavelength of maximum absorbance of the solubilizate when solubilized within the micelle. Utilizing this... 

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