Broadband probes

Fig. 6, aB-scan of a 15 mm thick sandwich with Nomex cores and GFRP-skins, shows clearly the depth of the two defects in the core [4]. A HILL-SCAN 3010 board and a broadband probe (0,8 to 3 MHz) were used. In regions without defects, the backwall-echo is indicated. 

The rf pulses for 27A1 NMR experiments were calibrated using an aqueous solution of A1C13. For the rf power level attenuated by 10 dB, the duration of the 180 "-pulse of the broadband probe was 60 ps. All solids imaging experiments were performed with t => 300 ps and the nominal flip angle a = 90°/(J + 1/2). The two pulses had the same amplitude and for 27A1 MRI were 10- and 20-ps long, respectively. 

Fig. 4. (a) 300 MHz proton spectrum and (b)-(e) selective reverse INEPT spectra of 28% menthone (Aldrich) in acetone-ds, measured using a 5 mm sample in the 10 mm broadband probe of a Varian Associates XL300 spectrometer using the sequence of fig. 1. The sample contains substantial quantities of isomenthone, seen clearly in the methyl region of trace (a). Spectra (b) to (e) used selective excitation of carbon sites 6, 7, 2 and 8, respectively, with delays 2r of 3.85, 3.85, 1.92 and 1.54 ms. 32 transients were used for each trace no spin lock pulses or 180° pulses were used. Traces (b) to (e) have a vertical scale lOOOx that of trace (a). No homodecoupling was used during acquisition. 

We performed femtosecond infrared pump-probe experiments, using pulses with a bandwidth of 200 cm"1 (FWHM). A small fraction of the infrared pulses was split off to obtain a broadband probe pulse, which was spectrally dispersed after interaction with the... 

The observed differences in the OH buildup rates at a given photolysis wavelength can be attributed to OH rotational levels having different parentages. For example, if higher-than-binary complexes yield mainly low N, this could be reflected in the product-state-selective measurements, even if the number of higher complexes is smaller than the number of binary complexes. In this case, there would be differences between results obtained with product state resolution versus those obtained by using a broadband probe. The latter would only be sensitive to the low N contribution in direct proportion to its fraction of the total product... 

We now discuss and review examples of studies conducted using the broadband probe pulse generation and detection methods described above. The examples presented here were chosen to provide the reader with a synopsis of the techniques and state-of-the-art performance of the tested array technologies. It is anticipated that these examples will generate an appreciation... 

The IR-2D spectroscopic technique applied in Section IV.C (30,42) utilized the frequency domain after selectively bleaching individual one-excitonic states using a narrowband intense pump pulse, a broadband probe pulse... 

NMR samples contained 0.6 ml receptor (0.5-2.0 mM) dissolved in refolding buffer (vide supra) with 10% DjO. One-dimensional F NMR spectra were obtained at 470 mHz on a General Electric GN 500 spectrometer fitted with a 5 mm F probe. Parameters included 16K data points, 3.0 second relaxation delay and 25 Hz linebroadening for processing spectra. T, relaxation times were measured by the inversion recovery method. The two-dimensional F NOESY NMR spectrum was obtained on a Varian Unity Plus 500 using the standard Varian pulse sequence. A total of 128 experiments with a mixing time of 0.3 seconds were performed with collection of 1024 data points. Quadrature detection in the second dimension was obtained through the method of States and Haberkom. C ( H NMR spectra were obtained on a Varian 500 Unity Plus fitted with a 10 mm broadband probe. 

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 primary disadvantages of cryogenic probes are that they are very expensive, require more physical infrastructure like chilled water lines than a conventional probe, and are difficult to install and remove. Most facilities with cryogenic probes keep them in dedicated instruments and only remove them for maintenance or repair. This works well for groups with similar samples and needs. Cryogenic probes typically have fixed frequencies and cannot replace the flexibility of broadband probes for unusual nuclei. 

High resolution solution state NMR spectra were obtained using a 10 mm broadband probe on a Bruker WM 500 spectrometer with a 45° flip angle, power-gated broadband decoupling and a relaxation delay of 6 seconds. 

P and Sn NMR spectra were recorded on a Varian XL 300 FT-NMR spectrometer equipped with a multinuclear broadband probe and operated at 121.42 and 111.86 MHz, respectively. P NMR spectra were recorded by setting triphenyl phosphate (in CDCI3) at (P) = — 18 ppm relative to 85% H3PO4 see J. Emsiey and D. Hall, The Chemistry of Phosphorus, Wiley, New York, 1976, p. 82. Upheld shifts are negative. 

Fig. 2.5. A comparison of the effect of extractants on solution P nuclear magnetic resonance spectra (Cade-Menun etal., 2002). The samples were a soil and a litter sample collected under stands of cedar in Washington, USA. The NaOH samples were extracted with 0.25 M NaOH, the Chelex samples were extracted with 0.25 M NaOH plus 6 1 Chelex to soil or litter (weight basis) and the EDTA samples were extracted with a 1 1 mix of 0.5 M NaOH plus 0.1 M Na2EDTA. Spectra were collected on a DRX-500 spectrometer with a 10-mm broadband probe, using a 90° pulse, 3.2 s pulse delay and 32°C temperature. See Cade-Menun et al. (2002) for more details.

Probe 5 mm or 3 mm CH dual probe, QNP probe, TXI probe, Broadband probe. Cryocooled probe in which the probe rf coil and the preamplifier are close to liquid helium temperature The sensitivity of H and is three to four times higher than that of a conventional probe. Significant reduction in time for 2D NMR experimentslD H can be obtained with as little as 10 ng of compound... 

HMBC-based experiments). From the 2D spectrum it was possible to directly assign the platinum resonances of the different isomers and hence determine the isomer ratios. These data were collected on a triple-channel instrument equipped with a Broadband probe for which the broadbanded channel had been tuned to Pt. 

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. 

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