Broadband probes phases

NMR Spectrometry. Liquid phase and NMR spectra were recorded on a Varian XL300 NMR spectrometer at carbon and nitrogen resonant fi equencies of 75.4 and 30.4 MHz, respectively, using a 10 mm broadband probe. Quantitative NMR spectra of the unreacted fulvic and humic acid samples were recorded in DMSO-d6, 99.9 atom % as previously described (23). INEPT (24) and ACOUSTIC (25) N NMR spectra were recorded on the aniline-reacted fulvic and humic acids. Refocussed INEPT (proton decoupled) spectra were recorded as previously described (9). ACOUSTIC spectra, with the exception of the bimessite catalyzed sample, were recorded with the use of paramagnetic relaxation reagent (100-200 mg chromium (III) acetylacetonate). Acquisition parameters included an 18,656.7 Hz spectral window (613.7 ppm), 0.5-s acquisition time, 45° pulse angle, 2.0-s pulse delay, and t delay of 0.1 ms. Neat formamide in a 5 mm NMR tube, assumed to be 112.4 ppm, was used as an external reference standard for all spectra. N NMR chemical shifts are reported in ppm downfield of ammonia, taken as 0.0 ppm. 

The absence of a, phase-matching condition means that it is also possible to use a fixed frequency pump laser with a broadband probe laser. This gives a complete Raman spectrum over the bandwidth of the probe laser (- 1000 cm l) which can be analysed using a spectrometer placed after the blocking polarizer, followed by an optical multichannel analyzer. 

The basic components of the solid state spectrometer are the same as the solution-phase instrument data system, pulse programmer, observe and decoupler transmitters, magnetic system, and probes. In addition, high-power amplifiers are required for the two transmitters and a pneumatic spinning unit to achieve the necessary spin rates for MAS. Normally, the observe transmitter for 13C work requires broadband amplification of approximately 400 W of power for a 5.87-T, 250-MHz instrument. The amplifier should have triggering capabilities so that only the radiofrequency (rf) pulse is amplified. This will minimize noise contributions to the measured spectrum. So that the Hartmann-Hahn condition may be achieved, the decoupler amplifier must produce an rf signal at one-fourth the power level of the observe channel for carbon work. 

Kuntz, in a series of papers (see Kuntz and Kauzmann, 1974), developed the use of magnetic resonance as a probe of the freezing of solvent in protein solutions. The nonfreezing water in a sample measured at - 35°C appears as an NMR signal that is sharp compared to the broadband response for the ice phase. The NMR method gives results for proteins and other macromolecules in close agreement with estimates of... 

This is an example of a general purpose high power spectrometer for solids. As sketched, it was set up for proton T measurements at 63 MHz but it has been used at various frequencies between 2 and 85 MHz by changing the transmitter and the receiver preamps as well as by using different probes. We do not heterodyne as in the previous example because the receiver is broadbanded. This does mean that the phase shift must be adjusted for each frequency. 

Before the tensile test the samples were investigated by ultrasonic transmission measurements as described in Section 25.2. The peak power of the RF-car-rier pulse (again 10-30 cycles, center frequency 2.25 MHz) was swept from 0 up to 3.6 kW and back to zero. The transmitted ultrasonic signal was detected by a broadband receiver probe, recorded, and Fourier-transformed. The dependence of the resulting amplitude and phase spectra on the transmitting pulse power was recorded. Figs. 25.11 and 25.12 show the results obtained for two of the specimens, one with a weak and one with a strong bond of 5.5 and... 

Combustion processes are driven by energy-releasing chemical reactions. Detailed knowledge of the chemical kinetics of these individual reactive steps is required input to combustion models. For more than a decade, elementary gas-phase reaction kinetics has been successfully studied with the flash photolysis/resonance fluorescence technique (1-8). Typically, following broadband photolysis of a molecular precursor, reactant decays have been measured under pseudo-first-order kinetic conditions with cw resonance lamp excitation of free radical fluorescence. Increased utilization of laser probes in kinetic studies is exemplified by the recent pulsed-laser photolysis/pulsed-laser-induced fluorescence experiments of McDonald, Lin and coworkers (9-13). 

Han and coworkers [38] determined the phase behavior of the ternary system consisting of [bmim][PFJ,TX-100, and water at 25 °C. By cyclic voltammetry method using potassium ferrocyanide, K Fe(CN)g, as the electroactive probe, the water-in-[bmim][PFJ, bicontinuous, and [bmim][PFJ-in-water microregions of the microemulsions were identified (Fig. 16.7). The hydrodynamic diameter of the [bmim] [PFJ-in-water microemulsions is nearly independent of the water content bnt increases with increasing [bmim] [PF ] content due to the swelling of the micelles by the IL. Sarkar and coworkers [39-41] reported the solvent and rotational relaxation studies in [bmim][PFJ-in-water microemulsions and water-in-[bmim][PFJ microemulsions using different types of probes, coumarin 153 (C-153), coumarin 151 (C-151), and coumarin 490 (C-490). The solvent relaxation time is retarded in the IL-in-water microemulsion compared to that of a neat solvent. The retardation of solvation time of water in the core of the water-in-IL microemulsion is several thousand times compared to pnre water. Nozaki and coworkers [42] reported a broadband dielectric spectroscopy study on a microemnlsion composed of water. 

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