Time Resolved Spectra

The sensitization of such films were smdied in detail by photocurrent spectra, time-resolved photocurrent measurements, and intensity-modulated photocurrent spectroscopy Visible light absorbed in the dyes led to the... 

The sensitization properties of such films were studied by photocurrent spectra, time-resolved photocurrent measurements and by intensity-modulated photocurrent spectroscopy (IMPS) [207, 209]. Visible light absorbed in the dyes led to the sensitization of ZnO in contact to an organic electrolyte as exemplary shown in Fig. 12. Many experiments were performed in a conventional three-electrode arrangement with the deposited hybrid thin films as working electrode, a Pt counter electrode and a Ag/AgN03 reference electrode. 0.5 M KI in acetonitrile/ ethylenecarbonate (1 4 by volume) was used as the electrolyte. Among TSPcMt... 

In this section we try to practically realize the idea of Ref. [20] by applying a train of subfemtosecond pulses composed of frequencies appropriate to photoelectron spectroscopy. Just as the vibrational progression is clearly recorded in conventional (time-independent) photoelectron spectra, time-resolved photoelectron spectroscopy with a well designed pulse train is anticipated to be able to monitor the electronic state progression along with signatures of the nuclear vibrational d mamics. 

However, luminescence lifetime, which is a measure of the transition probability from the emitting level, may be effectively used. It is a characteristic and an unique property and it is highly improbable that two different luminescence emissions will have exactly the same decay time. The best way for a combination of the spectral and temporal nature of the emission can be determined by laser-induced time-resolved spectra. Time-resolved technique requires relatively complex and expensive instrumentation, but its scientific value overweights such deficiencies. It is important to note that there is simple relationship between steady-state and time-resolved measurements. The steady-state spectrum is an integral of the time-resolved phenomena over intensity decay of the sample, namely ... 

Keywords Steady-state fluorescence spectra Time-resolved fluorescence decays Fluorescence anisotropy Huorescence quenching Nonradiative excitation energy transfer Solvent relaxation Excimer J and H aggregates... 

Figure 6. Time-resolved Fourier transform emission spectrum in the CO2 asymmetric stretch region from the HCCO + 02 reaction. Only signal from is observed. The fit to the data is...

Fig. 4 Fast time-resolved spectra of ethylene polymerization reaction on CO-reduced Cr/Si02 sample. Initial ethylene pressure was 10 Torr. Last spectrum after 15 s. Reprinted from [77]. Copyright (1994) by Elsevier...

Photoinduced oxidation of 1,4-dimethoxybenzene (DMB) and tetrahydrofuran (THF) by [Au(C N N-dpp)Cl]+ in acetonitrile upon UV/Vis irradiation have been observed. The time-resolved absorption spectrum recorded 12 (xs after excitation of [Au(C N N-dpp)Cl] with a laser pulse at 35 5 nm showed the absorption band of the DMB radical cation at 460nm, whereas upon excitation at 406 nm in the presence of THF, a broad emission characteristic of the protonated salt of 2,9-diphenyl-l,10-phenanthroline (Hdpp ) developed at 500 nm. 

Time-resolved resonance Raman (TR ) spectroscopy experiments were first reported in 1976 and used a 30 ns pulse radiolytic source to generate the intermediates that were then probed on the microsecond time-scale by a laser source to generate the TR spectrum. TR spectroscopy was then extended to study intermediates... 

Figure 3.30. (a) UV-vis absorption spectra of the HPAA product (solid line) and the HPDP substrate (dash line) in a H20/MeCN (1 1) mixed solvent, (b) Picosecond time-resolved resonance Raman (ps-TR ) spectra of HPDP obtained with a 267 nm pump and 200 nm prohe wavelengths in a HjO/MeCN (1 1) mixed solvent. Resonance Raman spectrum of an authentic sample of HPAA recorded with 200 nm excitation is displayed at the top. (Reprinted with permission from reference [49]. Copyright (2006) American Chemical Society.)... 

The simplest fluorescence measurement is that of intensity of emission, and most on-line detectors are restricted to this capability. Fluorescence, however, has been used to measure a number of molecular properties. Shifts in the fluorescence spectrum may indicate changes in the hydrophobicity of the fluorophore environment. The lifetime of a fluorescent state is often related to the mobility of the fluorophore. If a polarized light source is used, the emitted light may retain some degree of polarization. If the molecular rotation is far faster than the lifetime of the excited state, all polarization will be lost. If rotation is slow, however, some polarization may be retained. The polarization can be related to the rate of macromolecular tumbling, which, in turn, is related to the molecular size. Time-resolved and polarized fluorescence detectors require special excitation systems and highly sensitive detection systems and have not been commonly adapted for on-line use. 

IR spectrometer with the use of a simple time-resolved technique. 2D IR spectra are especially suited for elucidating various chemical interactions among functional groups. The type of information contained in a dynamic spectrum is determined by the selection of the perturbation (e.g. migration, drawing, aggregation, etc.). 

An interesting feature of polarized IR spectroscopy is that rapid measurements can be performed while preserving molecular information (in contrast with birefringence) and without the need for a synchrotron source (X-ray diffraction). Time-resolved IRLD studies are almost exclusively realized in transmission because of its compatibility with various types of tensile testing devices. In the simplest implementation, p- and s-polarized spectra are sequentially acquired while the sample is deformed and/or relaxing. The time resolution is generally limited to several seconds per spectrum by the acquisition time of two spectra and by the speed at which the polarizer can be rotated. Siesler et al. have used such a rheo-optical technique to study the dynamics of multiple polymers and copolymers [40]. 

Four different laboratories have built IR kinetic spectrometers for use with organometallic compounds. A fundamental feature of all these spectrometers is that the detector is AC coupled. This means that the spectrometers only measure changes in IR absorption. Thus, in the time-resolved IR spectrum, bands due to parent compounds destroyed by the flash appear as negative absorptions, bands due to photoproducts appear as positive absorptions, and static IR absorptions, due to solvents, for example, do not register at all. The important features of these spectrometers are listed in Fig. 2. Since three spectrometers have a line-tunable CO laser as the monochromatic light source, we begin with the CO laser. Then we look in more detail at spectrometers designed for gas phase and solution experiments. 

After the data are acquired, transient signals taken at individual wavelengths can be analyzed for kinetic information or an entire time-resolved spectrum can be synthesized. This is achieved by instructing the computer to assemble a point-by-point spectrum, corresponding to a particular delay time after the photolysis pulse. The spectrum is constructed out of points that are 4 cm-1 apart and is similar to a spectrum produced by a normal IR spectrometer but with 30 nsecond time resolution ... 

Figure 1 depicts the time resolved spectrum generated by photolysis of 30mtorr of Fe(C0>5 with a KrF excimer laser. As with all transient absorption experiments a major potential problem involves assigning the observed absorptions to specific species. For the... 

Figure 5. Transient time resolved spectrum following KrF photolysis of Cr(C0)6 with 5.0 torr Ar and 0.5 torr CO. The spectrum is displayed over a 10 fis range which is segmented into 10 equal time intervals. The first 3 intervals are labelled. (Reproduced with permission from reference 9. Copyright 1986 American Chemical Society.)...

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