Spectrum accumulation

Example The FD spectrum of a ruthenium-carbonyl-porphyrin complex shows an isotopic pattern very close to the theoretical distribution (Chap. 3.2.8). The loss of the carbonyl ligand chiefly results from thermal decomposition. A spectmm accumulated close to BAT (scans 19-25, EHC = 25-30 mA) is nearly free from CO loss while a spectrum accumulated of scans 30-36 (35 0 mA)... 

Spectrum Accumulation. The importance of studies at low radiation doses has already been indicated. Although radical yields are small at such doses, the high stability of modern spectrometers allows spectrum accumulation to be performed on low concentrations of radicals. This is illustrated in Figure 2 for... 

Perhaps the widest application is that of conventional high-resolution spectroscopy in solution for the purpose of learning in detail about polymer chain structure. In this field, proton NMR, formerly dominant, has given way to carbon-13 NMR with the development of pulse Fourier transform spectrometers with spectrum accumulation. Carbon spectroscopy is capable of giving very detailed and often quite sophisticated information. For example, a very complete accounting can be provided of comonomer sequences in vinyl copolymers and branches can be identified and counted, even at very low levels, in polyethylenes. 

For Raman scattering measurement, a freshly cleaved sample is directly illuminated with the Ar-ion laser, and the resulting spectrum, accumulated during 10 min, is shown in Fig. 23. The band at 1580 cm 1 corresponds to the in-plane C-C breathing mode of the whole graphite lattice, namely the E2g mode. The band at 2730 cm-1 is an overtone of a lower-energy vibration, and... 

Table 3.3. Correction of integrated centreband intensities to derive the actual aluminium site distribution in Y3AI5O12 derived from the MAS spectrum accumulated at 7.05 T spinning at 7 kHz shown in Figure 3.18C.

In addition, backward LP can be utilized for a completely different purpose. The first few data points at the beginning of the FID occasionally become corrupted if acquisition of the signal starts before pulse ringdown has faded to an acceptable level. In such a situation, a large baseline roll appears in the spectrum and renders it essentially useless. This result is especially disheartening when it occurs in a spectrum accumulated over a weekend. Still, the problem can easily be solved by replacing the first 5-10 data points with predicted points. Reweighting and a second FT result in an undistorted spectrum. 

Relative sensitivity in the spectrum accumulation mode for 10 shots 5.1 O 7 to 10 7... 

Figure 11.4 illustrates the measurement of peak intensity for the energy spectrometer on a spectrum accumulated for a preset livetime t. To improve the statistical precision, the counts under the peak are integrated over an energy interval AE. This interval is normally centered on the peak and corresponds to a number of channels r)p. For trace element work, AE is just slightly wider than the FWHM of the peak. The integral of the counts under the peak is... 

With energy-dispersive spectrometers it is convenient to carry out all data reduction on the spectrum accumulated for the preset livetime tt. Intensities are derived by dividing the net peak counts by the livetime. Thus, the net intensity in the peak is given by... 

NMR analysis. The spectra are recorded by a Varian DA-60-IL spectrometer. Deuterated dimethylformamide (DMF-d7) has been used as solvent. The copolymer solutions (10%) are heated at 130°C (internal reference Hexa-methyl-di-siloxane (HMDS), hmds = 0.05 ppm). Enhanced signal/noise ratios have been achieved by the Jeol-JR-Al Spectrum Accumulator and the decompositions and simulations of the complex pattern of methoxy and a-methyl resonances, by the Du Pont de Nemours, 310 Curve Resolver. Lorentzian curves, with a line width at half height of 2 Hz, have been used to simulate all the complex pattern of the methoxy and a-methyl resonances. The line width value has been determined from experimental measurements on NMR spectra. The broadening of the two a-methyl singlets from the s and h triad sequences are probably due to pentad effects [2, 5]. 

Spectrum accumulation for signal averaging Ernst, Rev. Sci. Instrum. 36 1689... 

Thanks to the development of Fourier transform instruments with spectrum accumulation, carbon spectroscopy, despite the low natural abundance of (1.1%), has become a method of fairly high sensitivity, able to establish the presence of structural features at a level of less than one carbon per 10,000. — Frank Bovey [ 10]... 

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