Electron absorption . linear

Polarized single crystal electronic absorption (linear di-chroism)... 

FIGURE 6. (a) Values of for the solvated electron absorption bands plotted against the mole fraction DMSO for DMSO/H O mixtures, (b) Photon energy of the absorption band maxima for the solvated electron in DMSO/HjO mixtures plotted against the bulk static dielectric constant (25 °C) of the mixture. Non-linear axes showing dielectric constant and mole fraction for (a) and (b) respectively are given as top abscissae. Reproduced by permission of the authors from Reference 30. 

The broad emission and low-fluorescence quantum yield of PPS suggested a distribution of trapping sites in the Si skeleton, which were also considered responsible for the lower-than-expected conductivity. The far-IR spectrum of PPS suggested the existence of cyclohexasilane rings connected by linear chains.361,362 Subsequent investigations by Irie et al. on the electronic absorption spectra of radical ions of poly(alkylsilyne)s were taken to indicate the presence of various cyclic silicon species, in corroboration of this conclusion.363 The large Stokes shift and broadness of the fluorescence emission indicate a range of fluorophore structures, different from the chromophore structures. This is... 

The addition of hydroxyde ion to nitrosobenzene produces azoxybenzene186. Three techniques (electronic absorption spectroscopy, linear sweep voltammetry and d.c. polarography) have been used to study the equilibrium between nitrosobenzene and hydroxyde ions. The probable reaction pathway to obtain azoxybenzene is indicated by Scheme 4. The importance of the nitroso group in the reduction of nitro derivatives by alkoxide ions, when the electron-transfer mechanism is operating, has been explained187. 

Probing Metalloproteins Electronic absorption spectroscopy of copper proteins, 226, 1 electronic absorption spectroscopy of nonheme iron proteins, 226, 33 cobalt as probe and label of proteins, 226, 52 biochemical and spectroscopic probes of mercury(ii) coordination environments in proteins, 226, 71 low-temperature optical spectroscopy metalloprotein structure and dynamics, 226, 97 nanosecond transient absorption spectroscopy, 226, 119 nanosecond time-resolved absorption and polarization dichroism spectroscopies, 226, 147 real-time spectroscopic techniques for probing conformational dynamics of heme proteins, 226, 177 variable-temperature magnetic circular dichroism, 226, 199 linear dichroism, 226, 232 infrared spectroscopy, 226, 259 Fourier transform infrared spectroscopy, 226, 289 infrared circular dichroism, 226, 306 Raman and resonance Raman spectroscopy, 226, 319 protein structure from ultraviolet resonance Raman spectroscopy, 226, 374 single-crystal micro-Raman spectroscopy, 226, 397 nanosecond time-resolved resonance Raman spectroscopy, 226, 409 techniques for obtaining resonance Raman spectra of metalloproteins, 226, 431 Raman optical activity, 226, 470 surface-enhanced resonance Raman scattering, 226, 482 luminescence... 

The nitrogen chemical shifts of the nitroso group show a roughly linear correlation with the energies of the lowest transitions observed in the electronic absorption spectra. The... 

The radiation passing thru the motor is picked up by a scintillation detector and the signal is fed to a strip chart recorder thru associated electronics. The linear attenuation (or absorption) coefficient (p) for any proplnt formulation can be determined exptly by the direct measurement of the decrease in the intensity of an attenuated beam of 7-radiation corresponding to the successive addition of incremental proplnt thicknesses placed in the path of the beam. By plotting the relative intensity (percent) of the attenuated beam on a log scale against the proplnt thickness on a linear scale, p can be determined from eq (1)... 

The electronic absorption spectra of PAHs have attracted great attention whereby different approaches toward classification of the particular bands have been proposed.142 A generally valid approach191 identifies (i) a-bands (Lb in the Platt nomenclature192) which relate to the longest wavelength absorption of benzene and are relatively weak and possess a distinct vibrational structure, (ii) p-bands (La) of medium intensity and are more sensitive to a linear annulation than the a-bands, and (iii) /1-bands (Ba, Bb) which are intense and have no vibrational structure. 

The oligomers 23 and 24a-c show enhanced solubility and increased glass transition temperatures when compared to their linear counterparts 25 and 26 (Scheme 3.10). No melting transition is observed for 23 whereas the linear molecule 25 (Scheme 3.10) melts at 254 °C. The electronic absorption spectra of the cruciforms 23 and 24a-c exhibit structureless, broad absorption peaks. Assuming a nonplanar ground state, the also featureless emission spectra indicate no significant increase of planarity upon photoexcitation. In addition, the cruciform molecules 23 and 24a-c show lower photoluminescence quantum yields (41-70%)... 

The electronic absorption spectroscopy of charge transfer (CT) complexes of donor molecules of n-, n- and cr-type (DX) with jt- and rr-acceptors (A = TCNE, I2 etc.) allows one to study the influence of the X substituents bonded to a donor centre, D, on the energies of charge transfer bands, hvcr129- The hvcr and Ip parameters are connected by a linear dependence given in equation 19. 

V-UV Application First Excited State of Linear Polyenes. The first electronic absorption band of perfect linear aromatic polyenes (CH)X, or perfect polyacetylene shifts to the red (to lower energies) as the molecule becomes longer, and the bond length alternation (BLA) would be zero. This was discussed as the free-electron molecular orbital theory (FEMO) in Section 3.3. If this particle-in-a-box analysis were correct, then as x > oo, the energy-level difference between ground and first excited state would go to zero. This does not happen, however first, because BLA V 0, next, because these linear polyenes do not remain linear, but are distorted from planarity and linearity for x > 6. 

Consider a linear calibration experiment, for example measuring the peak height in electronic absorption spectroscopy as a function of concentration, at five different concentrations, illustrated in Figure 2.5. A chemist may wish to fit a straight line model to the experiment of the form... 

Herein lies an opportunity for computing excitation spectra (and the actual CD intensity) from TDDFT linear response Once a response equation for /i(ffl) (or 4>(a>)]) has been derived, circular dichroism can be computed from an equation system that determines the poles of [> on the frequency axis, just like regular electronic absorption spectra are related to the poles of the electronic polarizability a [27]. Details are provided in Sect. 2.3. We call this the linear response route to calculating excitation spectra, in contrast to solving (approximations of) the Schrodinger equation for excited state and explicitly calculating excited state... 

Fig. 1 Top Behavior of the electronic linear chiroptical response in the vicinity of an excitation frequency. Re = real part (e.g., molar rotation [< ]), Im = imaginary part (e.g., molar ellipticity [0]). Without absorption line broadening, the imaginary part is a line-spectrum (5-functions) with corresponding singularities in the real part at coex. A broadened imaginary part is accompanied by a nonsingular anomalous OR dispersion (real part). A Gaussian broadening was used for this figure [37]. Bottom Several excitations. Electronic absorptions shown as a circular dichroism spectrum with well separated bands. The molar rotation exhibits regions of anomalous dispersion in the vicinity of the excitations [34, 36, 37]. See text for further details...

Linear molecules are the only exception to the Jahn-Teller effect. But linear molecules may also have instabilities in their degenerate electronic states and this is called the Renner-Teller effect. It was first described by Renner in a theoretical paper on the degenerate first excited electronic state of carbon dioxide [86], It took more than twenty years to find the first experimental evidence of this effect, in the electronic absorption spectrum of the NH2 radical [87], The NH2 radical has one electron on an orbital and thus a n electronic state... 

The electronic absorption characteristics of chromophores within potential gela-tors can provide an important experimental monitor of the microscopic environment in which they reside. This is especially true when the information includes optical rotatory dispersion (ORD) and circular dichroism (CD) data for potential gelalors that arc chiral. Dichroism relates to the absorptivity difference between the two components of circularly polarized light, w-hich constitutes the incident plane of linearly polarized light as described by the Kronig-Kramers transform. The intensity of UV/vis absorption depends on corresponding quantum transition. The wavelengths at which nonzero circular dichroism may be observable in the CD spectrum can be discerned from the shape of the absorption bands. The... 

The growth of fiberlike aggregates of optically active molecules [48], like those encountered with some optically active organogelators, is known to be accompanied by important CD modifications. CD data, free of linear dichroic effects, so as to avoid the contribution of macroscopic anisotropy, reveal chirality effects typical of helical structures. The electronic absorption spectra of the gelators indicate the wavelengths at which the electronic transitions occur and where dichroic effects have to be sought (unless selective reflection components... 

Just as the linear response of the medium displays a resonance in the vicinity of an electronic absorption, the non-linear properties also show resonant behaviour. These can be understood by extending the Lorentz model to the case of an anharmonic oscillator where the restoring force contains terms proportional to the square, cube, etc. of the displacement. Hence Equation (3.63) becomes ... 

Figure 3 Electronic absorption (A) and magnetic circular dichroism (B) spectra of the Type 1 Cu site of Achromobacter cycloclastes nitrite reductase (a) and spinach plastocyanin (b). Absorption data were obtained at 120 K for nitrite reductase and at 25 K for plastocyanin. MCD spectra were obtained at 4.2 K. Gaussian resolution of bands in the absorption spectra is based on a simultaneous linear least-squares fit of Abs, MCD, and CD data for each. MCD data from 5000 to 8000 cm have been multiplied by a factor of 5. (Reprinted with permission from Ref. 22. 1996 American Chemical Society)...

Conversion electrons are monoenergetic and exhibit a nearly linear absorption curve (Fig. 6.9), if their energy is >0.2 MeV. At energies <0.2 MeV the absorption curve deviates more or less from linearity. To obtain the effective range of conversion electrons, the linear part of the absorption curve is extrapolated to the intensity 7 = 0. 

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