Corrected absorption spectra

Figure 10.6 Corrected absorption spectra of primaquine, quinacrine, and quinine.

A plot of Esemiquinone vs X will constitute a corrected absorption spectrum of the semiquinone (Figure 3). Numerous studies have been made and corrected absorption spectra of the semiquinones have been determined ( Table 1). 

Figure 10. Corrected absorption spectra of the semi-oxidised 1,4- QH2-2S at ca.

We have conveyed some of the spirit and excitement of development and uses of TDDFT in this review. We explained what TDDFT is and where it comes from. While it often works well for many molecular excitations, its usefulness lies neither in high accuracy nor reliability but instead in its qualitative ability to yield roughly correct absorption spectra for molecules of perhaps several hundred atoms. We emphasize that there are usually many excitations of the same symmetry, all coupled together, and that imder these circumstances the theory will be of greatest use. TDDFT is now a routine tool that produces accurate results with reasonable confidence for many molecular systems. 

The total time required for this procedure is —20-30 hr. As pointed out by the checkers, it is recommended that the purity of [Ir(NH3)5Cl]Cl2 be checked prior to use. The electronic absorption spectrum reported by Schmidtke appears to, be that of a mixture of [Ir(NH3)sCl]Cl2 and tro/is-[Ir(NH3)4Cl2]Cl. The correct absorption spectrum is the same as reported by Blanchard and Mason. ... 

The PL spectrum and onset of the absorption spectrum of poly(2,5-dioctyloxy-para-phenylene vinylene) (DOO-PPV) are shown in Figure 7-8b. The PL spectrum exhibits several phonon replica at 1.8, 1.98, and 2.15 eV. The PL spectrum is not corrected for the system spectral response or self-absorption. These corrections would affect the relative intensities of the peaks, but not their positions. The highest energy peak is taken as the zero-phonon (0-0) transition and the two lower peaks correspond to one- and two-phonon transitions (1-0 and 2-0, respectively). The 2-0 transition is significantly broader than the 0-0 transition. This could be explained by the existence of several unresolved phonon modes which couple to electronic transitions. In this section we concentrate on films and dilute solutions of DOO-PPV, though similar measurements have been carried out on MEH-PPV [23]. Fresh DOO-PPV thin films were cast from chloroform solutions of 5% molar concentration onto quartz substrates the films were kept under constant vacuum. 

Figure 15-12. Spectrally resolved pliotocurrent of a ITO/PPV/Mg photodiode at dilTcrcnt bias after correction for dark current, light source, and monochromator response, and normalization to the same peak value. The broken line is the normalized absorption spectrum of PPV (reproduced by permission of the Institute of Physics from Ref. 143)).

Fig. 6.2.4 Change in the absorption spectrum of pholasin (14.5 p,M) caused by the luminescence reaction catalyzed by Pholas luciferase (1.1 p.M). The curve shown is the differential spectrum between a cell containing the mixture of pholasin and Pholas luciferase (0.9 ml in the sample light path) and two cells containing separate solutions of pholasin and the luciferase at the same concentrations (in the reference light path), all in 0.1 M Tris-HCl buffer, pH 8.5, containing 0.5 M NaCl. Four additions of ascorbate (3 iM) were made to the sample mixture to accelerate the reaction. The spectrum was recorded after 120 min with a correction for the base line. From Henry and Monny, 1977, with permission from the American Chemical Society.

Raman spectra of S2 in its triplet ground state have been recorded both in sulfur vapor and after matrix isolation using various noble gases. The stretching mode was observed at 715 cm in the gas phase [46], and at 716 cm in an argon matrix [71]. From UV absorption and fluorescence spectra of sulfur vapor the harmonic fundamental mode of the S2 ground state was derived as t e = 726 cm . The value corrected for anharmonicity is 720 cm [26, 27]. Earlier reports on the infrared absorption spectrum of 2 in matrix isolated sulfur vapor [72] are in error the observed bands at 660, 668 and 680 cm are due to S4 [17] and other species [73]. 

For several technical reasons, it is not possible to acquire NMR data with perfect phase. One reason is the inability to detect XY magnetisation correctly another is the fact that we are unable to collect the data as soon as the spins are excited. These limitations mean that we have to phase correct our spectrum so that we end up with a pure absorption spectrum. What we don t want is a dispersion signal (see Spectrum 4.2). 

Photophysical Processes in Dimethyl 4,4 -Biphenyldicarboxy-late (4,4I-BPDC). The ultraviolet absorption spectrum of dimethyl 4,4 -biphenyldicarboxyl ate was examined in both HFIP and 95% ethanol. In each case two distinct absorption maxima were recorded, an intense absorption near 200 nm and a slightly less intense absorption near 280 nm. The corrected fluorescence excitation and emission spectra of 4,4 -BPDC in HFIP at 298°K shows a single broad excitation band centered at 280 nm with a corresponding broad structureless emission band centered at 340 nm. At 77°K, the uncorrected phosphorescence spectra shows a single broad structureless excitation band centered at 298 nm, and a structured emission band having maxima at 472 and 505 nm with a lifetime, t, equal to 1.2 seconds. 

Photophysical Processes in Pol,y(ethy1eneterephthalate-co-4,4 -biphenyldicarboxyl ate) (PET-co-4,4 -BPDC). The absorption and luminescence properties of PET are summarized above. At room temperature the absorption spectrum of PET-co-4,4 -BPDC copolymers, with concentrations of 4,4 -BPDC ranging from 0.5 -5.0 mole percent, showed UV absorption spectra similar to that of PET in HFIP. The corrected fluorescence spectra of the copolymers in HFIP exhibited excitation maxima at 255 and 290 nm. The emission spectrum displayed emission from the terephthalate portion of the polymer, when excited by 255 nm radiation, and emission from the 4,4 -biphenyldicarboxylate portion of the polymer when excited with 290 nm radiation. 

Interferences in atomic absorption measurements can arise from spectral, chemical and physical sources. Spectral interference resulting from the overlap of absorption lines is rare because of the simplicity of the absorption spectrum and the sharpness of the lines. However, broad band absorption by molecular species can lead to significant background interference. Correction for this may be made by matrix matching of samples and standards, or by use of a standard addition method (p. 30 et seq.). 

The values of ftot for various benzotriazole compounds in a range of solvents are listed in Table II. Values of the fluorescence quantum yield for TIN and TINS, corrected for the absorbance by their non-fluorescent, planar conformers at the excitation wavelength, are listed in Table III. In all the benzotriazole solutions examined, maximum fluorescence emission was observed at about 400 nm indicating that this emission originates from the non proton-transferred species. This was confirmed by examination of the fluorescence excitation spectrum which corresponds to the absorption spectrum of the non-planar form of the molecule. 

The variations in fluorescence intensity as a function of the excitation wavelength XE for a fixed observation wavelength represents the excitation spectrum. According to Eq. (3.20), these variations reflect the evolution of the product /0(FE)A(AE). If we can compensate for the wavelength dependence of the incident light (see Chapter 6), the sole term to be taken into consideration is A(AE), which represents the absorption spectrum. The corrected excitation spectrum is thus identical in... 

Steady-state method 2 comparison between the absorption spectrum and the excitation spectrum (through observation of the acceptor fluorescence) The corrected excitation spectrum is represented by... 

Figure 8.2 presents the fluorescence of pyrene on silica gel. The loading is low so that pyrene is predominantly adsorbed as nonaggregated monomers (Mi). The backward fluorescence spectrum Fb of this sample is very comparable to the spectrum in polar solvents and not distorted by reabsorption. However, the forward spectrum Ft is almost completely suppressed in the region of overlap with the o -transition and hot sidebands of the weak first absorption band Si. The absorption coefficients of the sample vary widely from k" = 0.1 cm 1 (Si-band, Aa = 350-370 nm) to k = 25 cm-1 (S2-band, 1 290-340 nm), and in a first approximation the excitation spectrum of Fh reflects this variation correctly (Figure 8.2, left). The Ff-excitation spectrum, however, has only little in common with the real absorption spectrum of the sample. 

To conclude, the results presented in this section demonstrate that the semiclassical implementation of the mapping approach is able to describe rather well the ultrafast dynamics of the nonadiabatic systems considered. In particular, it is capable of describing the correct relaxation dynamics of the autocorrelation function as well as the structures of the absorption spectrum of... 

Group theory has been useful in chemistry in several ways. First, it has provided simple, qualitahve explanations for the behavior of matter. For example, why can the states of electrons in any atom be classified, to a good approximation, by the four quantum numbers n, I, rrii and m Why, in their ground states, is BeH2 a linear molecule but H2O bent Why do certain transitions not appear in an absorption spectrum Lengthy computations can provide correct but uninformative answers to these questions group theory can provide perspicuous explanations of the factors that determine these answers. 

We used the dielectric function e of bulk MgO calculated from oscillator parameters determined by Jasperse et al. (1966), together with the dielectric function em of the KBr matrix given by Stephens et al. (1953) (corrected by June, 1972), to calculate the absorption spectrum (12.37) of a dilute suspension of randomly oriented MgO cubes. These theoretical calculations are compared with measurements on well-dispersed MgO smoke in Fig. 12.16c. Superimposed on a more or less uniform background between about 400 and 700 cm-1, similar to the CDE spectrum, are two peaks near 500 and 530 cm- , the frequencies of the two strongest cube modes. It appears that for the first time these two modes have been resolved experimentally. If this is indeed so we conclude that the widths of individual cube modes are not much greater than the width of the dominant bulk absorption band. Genzel and Martin (1972)... 

In many cases, the lack of correction for reflection will not affect the shape of the optical spectrum very much, but it will just give an inflated value for absorption. However, there are frequently cases where the shape of the absorption spectrum is also appreciably changed after the reflection correction is carried out. Also, if the primary absorption is a weak one, then correction for reflection, and in particular for scattering, is crucial, since the absorption may be masked by these effects. 

In reality the individual lines obtained after the Fourier transformation are composed of both absorptive A(f) and dispersive D(f) components. This non-ideality arises because of a phase shift between the phase of the radiofrequency pulses and the phase of the receiver, PHCO, and because signal detection is not started immediately after the excitation pulse but after a short delay period A. Whereas the effect of the former is the same for all lines in a spectrum and can be corrected by a zero-order phase correction PHCO, the latter depends linearly on the line frequency and can be compensated for by a first-order phase correction PHCl. Both corrections use the separately stored real and imaginary parts of the spectrum to recalculate a pure absorptive spectrum. 

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