Electronic Transition Absorption

Figure 3.10 The electronic transitions [absorption in (a)] of small molecules show vibrational and rotational lines in addition to the purely electronic spectrum, (b) Luminescence emission is resonance fluorescence (f), and chemical reactions (R) can originate from several excited states...

If we limit our description to the initial step of the whole process, i.e. the vertical electronic transition (absorption and emission), we can safely assume a Franck-Condon like response of the solvent, exactly as for the solute molecule the nuclear motions inside and among the solvent molecules will not be able to follow immediately the fast changes in the solute electronic charge distribution and thus the corresponding part of the... 

Hgl2 is also a typical semiconductor material, and it is also easy to vaporize after thermal treatment. Therefore, Hgl2 may be loaded into various zeolites through a vapor-transportation approach. Because of the confinement of the zeolite framework, Hgl2 in zeolites may exhibit distinct quantum-size effects. The electronic transition absorption spectrum of Hgl2 loaded in AlPOs-5 single crystals shows an apparent blue-shift, and in... 

Electronic transition absorption losses of organic materials in the visible wavelength region are caused by multiple bonds (such as double bonds, triple bonds, and aromatic rings) whose electronic transitions involve the electrons in the rc-bonds. The accurate estimation of oteiec therefore requires very detailed quantum mechanical calculations which can use up large amounts of computer time. Instead, a simple empirical correlation is used for CKeiec-... 

Ax 1 cm, the uncertainty of the momentum, Ap, is small. Thus, the momentum is a good quantum number and its conservation has to be obeyed in electronic transitions. In silicon, which has an indirect band gap, the recombination of electrons and holes requires a creation or annihilation of phonons and is therefore predominantly of non-radiative nature.If, however, the size of an Si nanocrystal approches 1 nm. Ax 1 nm and Ap spans a significant part of the Brillouin zone. The momentum conservation is relaxed and electronic transitions (absorption of a photon with the formation of an electron-hole pair or their radiative recombination) become efficient. 

When a solvent molecule becomes attached to a solute (which may be a reactant or a transition state), the electrons in frontier orbitals are affected to some extent. Therefore, when the solvated species undergoes an electron transition, absorption occurs at wavelengths that vary somewhat with the nature of the solvent. It is possible to make use of the spectral shifts (the so-called solvatochromic ect) to give some indication of the strength of solvent-solute interactions. 

Electron transition Absorption region (nm) Extinction coefficient (L mol cm )... 

The absorption of light in POF materials depends on its frequency or wavelength because materials have various energy levels that are involved in absorption transitions. In the light wavelengths used for data communication with POFs, the intrinsic absorption losses are caused by electronic transition absorptions and/or molecular vibration absorptions. The electronic transition absorption peaks typically appear at ultraviolet wavelengths, and their absorption tails influence the transmission losses of POFs. For example, a POF with a poly(methyl methacrylate) (PMMA) core exhibits n- i transitions due to the ester groups in methyl methacrylate (MMA) molecules, n-a transitions of S-H bonds in chain-transfer... 

Every material absorbs light energy, whose amount depends on the wavelength and the material. Intrinsic absorption loss in POFs is caused by electronic transitions and molecular vibrations. Electronic transition absorption results from transitions between electronic energy levels of bonds within the materials. The absorption of photons causes an upward transition, which leads to excitation of... 

A UV-visible spectrometer is used to measure electronic transition absorption. Electronic transition, UV absorption, loss values for core-composing materials, such as monomer, polymerization initiators, and chain transfer agents, and for polymer rods decrease exponentially with wavelength. A linear relationship is observed for PMMA raw materials. However, PMMA shows an absorption maximum near 360 nm, and linear parts are observed in both lower and higher wavelength regions. This absorption maximum may be derived from residual azo compound. In these cases, a linear part obeys the so-called Urbach rule i.e., electronic transitional loss values,... 

---