Near-UV absorption

Figure 1-3. Comparison between experimental and theoretically derived spectra for prephenate anion in solution. The vertical lines correspond to the theoretical spectrum for 12 conformers (3 lines for each) with intensities computed as described in the main text. The experimental spectrum is presented as a dark line (with the highest energy intensity also normalized to 1). The inset shows the near-UV absorption in greater detail. Adapted from Ref. [18]...

In this molecule the diene moiety assumes the C2V symmetry and the prominent feature of its near-UV absorption spectrum is the 240 nm band (fimax 3500), assigned6 to the same transition r - jt L, now characterized by xAi - lB2 symmetry in the C2V point group (see Appendix, Section V). 

The ligands have n and a orbitals, but only the n orbitals are spectroscopically important for visible and near-UV absorptions and emissions. There are both n bonding and n antibonding (n) levels. The n bonding levels are filled. 

Very intense and sharp near-UV absorption bands due to radical ions of polysilanes [53a,b] and polygermanes [53c] were observed by nanosecond pulse radiolysis. Broad visible and IR absorption spectra due to the radical ions of polysilyne [54] and polygermyne [54] were also observed. Very systematic pulse radiolysis studies on many different kinds of polysilanes [55] have been made by our improved nanosecond pulse radiolysis system over a wide range of... 

Bongartz, A., J. Karnes, F. Welter, and U. Schurath, Near-UV Absorption Cross Sections and Trans/Cis Equilibrium of Nitrous Acid, . /. Phys. Chem., 95, 1076-1082 (1991). 

Analysis of the data of Table 1 verifies the same finding that the shift of the near-UV absorption band of singlet arylnitrenes correlates with the shift of the intense near-UV absorption band of triplet nitrenes. Furthermore, the ort/io-substituents influence the absorption spectra of singlet and triplet phenylnitrenes more significantly than do para-substituents. 

The near UV absorption spectra of cytosine, cytidine, and their derivatives have been measured in different solutions and in the solid state. Early works by Stimpson and O Donnell38 were thought to confirm the previous conclusion from IR evidence that cytosine exists in the lactim-amine form 1. However, all later UV studies indicate that the predominating form both of cytosine and cytidine is lactam-amine... 

Figure B3.5.2 The two near-UV absorbance transitions for tryptophan. The near-UV absorption spectrum for A/-stearyl tryptophan n-hexyl ester dissolved in methylcyclohexane at 24°C (solid line) has been resolved into the 1La and 1Lb bands. (Drawn from Strickland, 1974.)...

According to the formula (7) absorption spectrum for conductivity electrons in bulk metal should be a smooth curve down to co->0. Ag film in the near UV range demonstrates spectrum of such type. Appearance of a near UV absorption peak in a spectrum of M nanocrystal is caused by the surface charges that resulted from displacement of conductivity electrons under action of an external field. These charges create in a nanocrystal the internal field directed against external one [16]. For conductivity electrons this internal field plays a role of quasi-elastic bonds between valent electrons and cations in a crystal lattice. 

The photochemistry of poly(di-n-hexylsilane) (PDHS) has been investigated by excimer laser flash photolysis20. Transient absorptions were found to be strongly dependent on the solvent employed and the near-UV absorptions at 385 and 360 run observed in cyclohexane and tetrahydrofuran, respectively, were ascribed to polysilylated silyl radicals, while that at 345 nm observed in dichloromethane was attributed to the radical cations of PDHS formed during the electron photoejection process. 

Fig. 11 The effect of polarized photolysis on the near-UV absorption of Cr(CO)5N2 in pure N2 (a) after 20 min unpolarized photolysis X = 314 nm and photolysis with X = 367 nm, (b) with vertically polarized photolysis 20 min, (c) with horizontally polarized photolysis 30 min, vertically polarized photolysis 15 min solid line) spectrum polarized vertically, broken line) spectrum polarized horizontally. Adapted from [24]...

The FT direct absorption spectra [28] of OCIO provide an example of the capabilities of FT spectroscopy in the visible and ultraviolet regions for the study of short-lived species. In Figure 14, part of the near-UV absorption spectrum is... 

Near UV Absorption The First Singlet 7777 Excited States... 

Ion-pair acidity is an important parameter to probe highly diluted solutions, as demonstrated by the sophisticated visible or near-UV absorption methods developed mainly by Streitwieser and coworkers. This analytical approach afforded the pXa values and aggregation states of a large set of cesium and lithium enolates. Its principle relies... 

The synthesis of the iridium(III) azide complex (Bu N)3[Ir(N3)6] occurs via reaction (75). The visible and near-UV absorption and reflection spectra of this complex have been recorded the assignment of bands in this and rhodium(III) azide complexes has led to the location of the Nf ligand in the spectrochemical and nephelauxetic series.283... 

Bames, I., K. H. Becker and T. Zhu Near UV absorption spectra and photolysis products of difunctional organic nitrates, J. Atmos. Chem. 17 (1993) 353-373. 

Consider the absorption spectrum of naphthalene (Figure 4.16) as an example. To predict the near-UV absorption bands, we need to consider only the four inner HMOs fiy to ij/ 2, which are shown on the left-hand side of Figure 4.26. On the right, the four lowest singly excited configurations are shown and their energies relative to the ground state... 

Near-UV absorption spectra of barbiturates depend on the type of substitution and the state of ionization of the molecule.52-54 Absorption bands at — 210 nm for undissociated compounds are shifted to 240-270 nm... 

The low-lying states responsible for the visible-near UV absorption and photo physical/chemical behaviour of mixed-ligand transition metal carbonyls M(CO)5L (Cr, Mo or W in d6 configuration, L=pyridine derivative or piperidine) were usually interpreted in terms of interplaying low-lying MLCT and Metal Centred (MC) electronic transitions [6]. According to recent theoretical studies the interpretation based on the assignment of weak spectral features to MC transitions is not necessarily correct DFT [88] and CASSCF/... 

When EB is protonated leading to ES, a continuous shift of the exciton band from 2 to 1.5 eV is observed, together with the growth of the polaron band, due to the formation of within-gap new defects levels. The polaron state with unpaired spin, (that is to say the isolated polaron) has been determined by Electron Spin Resonance at 2.75 eV when the level of protonation increases up to the formation of two associated polarons, the spin resonance disappears, while the peak shifts up to 3.1 eV [51]. In ES, beside the polaron lattice peak at (on an average) 2.9 eV, a new absorption centred at 1.0 eV attributed to intrachain ffee-carrier excitation appears also [52]. The near-UV absorption weakens, since the metallic character of ES is inconsistent with the keeping of a 7t —> tt transition. 

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