Time-resolved spectroscopies spectra

The Wheland intermediate in equation (87) is identified by time-resolved spectroscopy as follows.247 Laser excitation of the EDA complex of NO+ with hexamethylbenzene in dichloromethane immediately generates two transient species as shown in the deconvoluted spectrum in Fig. 20. The absorption band at lmax = 495 nm is readily assigned to the cation radical of... 

Luminescence of Pr + in zircon is very difficult to detect under UV excitation even by time-resolved spectroscopy. The reason is that it has a relatively short decay time similar to those of radiation-induced centers. Visible excitation, which is not effective for broadband luminescence, allows the revealing of Pr + luminescence lines, using high-resolution steady-state spectroscopy. Under such experimental conditions each element has individual lines, enabling confident identification of the spectrum to be possible (Gaft et al. 2000a). Only if radiation-induced luminescence in zircon is relatively weak, the lines of Pr may be detected by UV excitation (Fig. 4.38c). 

Figures 4.31a,b represent narrow luminescence hnes detected in barite by time-resolved spectroscopy. Much weaker lines at 446 and 672 nm accompany the strongest one at 588 nm. They have a relatively short decay time of 5 ps and emphasized in the spectrum with short gate. Such a combination of spectral and kinetic properties is not suitable for any trivalent REE besides P j2 f9/2...

One of the most spectacular observations in time-resolved emission spectroscopy is the rise and decay of molecular and excimer (or exciplex) spectra, illustrated in Figure 7.35(b). The structured molecular emission decreases immediately while the excimer emission increases up to a time of tens of ns, depending on the concentration. At longer times only the broad red-shifted excimer spectrum is observed. In Figure 7.35(b) the steady-state spectrum is shown in white this represents of course the integration of all the instantaneous spectra which can be obtained only through time-resolved spectroscopy. 

TNP-ATP complex obtained by the single-molecule time-resolved spectroscopy, together with a fluorescence decay curve of TNP-ATP obtained by a bulk measurement. Both curves were well fitted to biexponential functions. The instrument-response function in 195-ps fwhm is also displayed. (B) Representative fluorescence spectrums of two individual enzyme-TNP-ATP complexes showing different emission peaks. A fluorescence spectrum of TNP-ATP obtained from a bulk measurement is also displayed for comparison. All spectrums were normalized to unity at their maximum. (From Ref. 18.)... 

The reactive intermediates leading to the (charge-transfer) photodecomposition of the 6w(arene)iron(II) acceptor are revealed by picosecond time-resolved spectroscopy. For example, photoexcitation of the CT absorption band of the ferro-cene-(HMB)2Fe complex (HMB = hexamethylbenzene) with the second harmonic output (at 532 nm) of a mode-locked Nd YAG laser (25-ps pulse width) generates a transient spectrum with an absorption maximum at 580 nm (see Figure 11 A). Careful deconvolution of this absorption spectrum reveals the superposition of the absorption bands of ferrocenium (Imax = 620 nm, e = 360 cm [162]) and (HMB)2Fe+ (2 ,ax = 580 nm, = 604 M" cm" [163]). 

Fig. 9. (A) Absorption spectrum of Rb. sphaeroides used as a reference to show the Qx and Qy bands of the primary donor (P), BChl [B] and bacteriopheophytin [BO] (B) Femtosecond absorption changes at 920 (a), 785 (b) and 545 nm (c) vs. the delay time of the monitoring pulse measured at room temperature, and (C) absorption changes at 920 (a) and 794 nm (b) measured at 25 K. Figure source (A) see Fig. 7 (B) Holzapfel, Finkele, Kaiser, Oesterheldt, Scheer, Stilz and Zinth (1990) Initial electron transferin the reaction center from Rhodobacter sphaeroides. Proc Nat Acad Sci, USA 87 5170 (C) Zinth and Kaiser (1993) Time-resolved spectroscopy of the primary electron transfer in reaction centers of Rhodobacter sphaeroides and Rhodopseudomonas viridis. I n JR Norris and J Deisenhofer (eds) The Photosynthetic Reaction Center, Voi il, p 82. Acad Press.

These interpretations were supported by time-resolved spectroscopy. Laser flash photolysis of 4 in CH2C12 produces a transient spectrum (Figure 11) very similar to that obtained by flash photolysis of phenyl azide (Figure 8) and is therefore attributed to pentafluorodehydroazepine. Similar results were obtained in acetonitrile and tetrahydrofuran. However LFP of 4 in methanol gives an entirely different transient spectrum. (Figure 12). The... 

Electron transfercan be studied by time-resolved spectroscopy (Section 14.6e). The oxidized and reduced products often have electronic absorption spectra distinct from those of their neutral parent compounds. Therefore, the rapid appearance of such known features in the absorption spectrum after excitation by a laser pulse may be taken as indication of quenching by electron transfer. 

In the normal scan, points (retardation, intensity) are collected at a constant mirror velocity, that is along the diagonal of the plot in Fig. 14. In the Time Resolved Spectroscopy (TRS) step-scan mode, the data points at a single time are obtained at each retardation by repeating the number of scans (Fig. 14), to give, when transformed, single beam spectra at each time interval. These are then normalized to the reference spectrum to give the set of time-resolved reflectance spectra. 

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