Signal half width

Structure Chemical shifts S (p.p.m.) Reference signal Half-width (Hz) Solvent Ref... 

Fig. 3.6. Essential signal parameters zA signal position, yA signal (gross) intensity, signal background, fwhm(z) full width at half maximum (signal half width), fwb(z) full width at background...

In case of variable signal half-width Az as shown in Fig. 7.11b the following general expression applies (Danzer [1975]) ... 

In the case of constant signal half-width it results in Eq. (7.53) whereas, in the case of constant resolution R(z)y it follows that (Kaiser [1970] Danzer [1975])... 

In a net effect, the pulse repetition times in flowing systems can be reduced to the decrease in the apparent spin-lattice relaxation times Tifiow, whereas at a given detection volume an increase in flow rate leads to an increase in the signal half-width W due to the decrease of r2fi0w... 

It is well known that coals start to soften and melt at about 400 °C and then to cake and carbonize at more than 450 °C. A solid echo pulse sequence with a refocusing of 4 ps was used to minimize the loss of signal due to the dead time of the NMR coil. Figure 33 shows the variations in the rates and their signal half-widths at half-height for both components between 25 °C and 550 °C for the three kinds of coal obtained by the H wide line method. 

Thus the mobile component increases at the maximum mobility temperature giving a signal half-width for the mobile component which decreases at this temperature. Hence the unsoftened area becomes smaller and the softening and melting phenomena accelerate as the time of coking increases. 

In contrast to conventional NMR measurements, in flowing systems the sample has a defined dwell time x in the NMR coil. This dwell time is defined by the ratio of detection volume to flow rate and affects the relaxation times Tj and Ti as well as the signal intensity and signal half width ... 

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