Rapid-scan excitation,

In wide sectors of industry there is a growing need of inspection methods which go without liquid coupling media. The excitation of bulk and surface waves by means of air-coupled ultrasonic probes is therefore an attractive tool for NDE. This is tme e.g. for the rapid scanning of large composite structures in the aerospace industry [1]. In other cases, the use of liquid couplants is prohibitive like the thickness measurement of powder layers. 

All ILs showed a rich photochemistry after UV photolysis leading to the buildup of various long-lived intermediate products as evidenced from the observation that ILs turn yellow upon continuous irradiation. On the other hand, exposing ILs to short excitation pulse (a rapid-scan method) significantly suppressed the formation of halides [22]. 

Wt-GFP was expressed in E. coli and purified as described in Ref. [4]. Time- and frequency resolved pump-probe transients were recorded with 40-fs, 400-nm excitation pulses and probe pulses with durations of approximately 40 fs throughout the visible spectral range. Since photo-conversion strongly alters the GFP response, rapid scan data acquisition was performed... 

Fourier transform NMR spectroscopy, on the other hand, permits rapid scanning of the sample so that the NMR spectrum can be obtained within a few seconds. FT-NMR experiments are performed by subjecting the sample to a very intense, broad-band, Hl pulse that causes all of the examined nuclei to undergo transitions. As the excited nuclei relax to their equilibrium state, their relaxation-decay pattern is recorded. A Fourier transform is performed upon this relaxation-decay pattern to provide the NMR spectra. The relaxation-decay pattern, which is in the time domain, is transformed into the typical NMR spectrum, the frequency domain. The time required to apply the Hl pulse, allow the nuclei to return to equilibrium, and have the computer perform the Fourier transforms on the relaxation-decay pattern often is only a few seconds. Thus, compared to a CW NMR experiment, the time can be reduced by a factor of 1000-fold or more by using the FT-NMR technique. 

Transient absorption spectroscopy, wherein one measures the electronic absorption spectrum of a molecule in an excited state, is still in its infancy, but the growing availability of ultra-high-speed, rapid-scan spectrometers augurs well for this area of spectroscopy. Thus one may, in the future, routinely probe excited state absorption spectra as well as ground state absorption spectra. The former can be expected to be as valuable in obtaining information about the excited state as is the latter for the ground state. 

The atmospheric chemistry of trifluoroacetyl radical CF3CO is not well known. It was implicated to explain the products observed98 in photolysis of hexafluoroacetone in the presence of Br2 and Cl2, but its first direct observation came from rapid-scan infrared spectroscopic studies in a matrix99, and more recently its laser-induced fluorescence spectrum has been observed100 the band origin for the first excited state of the radical appears at 384 nm. A weak UV absorption band which onsets at 250 nm and continues to increase in intensity below 200 nm has been attributed to CF3C0101. 

Fourier transform mass spectrometry (FTMS) was first described by Comisarow and Marshall in 1974 [59,60] and was reviewed by Amster [61] in 1996 and by Marshall et al. [62] in 1998. This technique consists of simultaneously exciting all of the ions present in the cyclotron by a rapid scan of a large frequency range within a time span of about 1 ps. This induces a trajectory that comes close to the wall perpendicular to the orbit and also puts the ions in phase. This allows transformation of the complex wave detected as a time-dependent function into a frequency-dependent intensity function through a Fourier transform (FT), as shown in Figures 2.60 and 2.61. 

Fluorescence detection is not very often used in phenolic acid analysis, but, in cases when very low concentrations of some analytes or many interfering compounds are present in extracts, the combination of UV and DAD with fluorescence detector could be valuable. However, the same problems could arise as in the UV detection, i.e., establishing the correct excitation and emission wavelengths, as large differences for several phenolic acids were observed. In this case, the rapid scanning... 

Figure 5.14. Schematic diagram of a fluorescence detector with rapid scanning monochromators for programmable selection of excitation and emission wavelengths.

The lifetimes of the sublevels of the excited triplet state of the Rh-trisdiimine complexes have been determined using the microwave recovery and adiabatic rapid passage techniques mentioned in Sect. 4.2. At (pumped) liquid helium temperatures it turned out that the triplet state sublevels have distinct lifetimes. As an example, we show in Fig. 8 the optically detected adiabatic transient signal as monitored for the zero-field D -1 resonance, at 2320 MHz, of the photo-excited [Rh(bpy)3] (0104)3 single crystal, at 1.4 K. The microwave frequency scan was at a rate of 2 x 10 Hz/s. Similar transients were obtained by rapid scans through the zero-field microwave transitions for the other compounds of the [Rh(phen)u(bpy)3 n] (0104)3 series. The transients fitted a biexponential function of the form... 

Both instrument design and capabilities of fluorescence spectroscopy have greatly advanced over the last several decades. Advancements include solid-state excitation sources, integration of fiber optic technology, highly sensitive multichannel detectors, rapid-scan monochromators, sensitive spectral correction techniques, and improved data manipulation software (Christian et al., 1981 Lochmuller and Saavedra, 1986 Cabaniss and Shuman, 1987 Lakowicz, 2006 Hudson et al., 2(X)7). The cumulative effect of these improvements have pushed the limits and expanded the application of fluorescence techniques to numerous scientific research fields. One of the more powerful advancements is the ability to obtain in situ fluorescence measurements of natural waters (Moore, 1994). 

Multielemental Analysis Atomic emission spectroscopy is ideally suited for multi-elemental analysis because all analytes in a sample are excited simultaneously. A scanning monochromator can be programmed to move rapidly to an analyte s desired wavelength, pausing to record its emission intensity before moving to the next analyte s wavelength. Proceeding in this fashion, it is possible to analyze three or four analytes per minute. 

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