Line width saturation broadened

This Doppler width can be avoided by typical sub-Doppler laser spectroscopy techniques. Laser saturation spectroscopy with a resolution close to the natural line width was used for a test of Special Relativity at the ESR. For such sub-Doppler resolution one must also take into account the small additional broadening and shift arising from the angle 0 between laser beam and ion beam in the Doppler formula. At an interaction length of 10 meters and more, angles are easily controlled to be better than 1 mrad. This limits a possible shift, which enters by... 

The dipole-dipole coupling and the inhomogeneities are responsible for line broadening in a NMR spectrum when the molecular motions are slow. From line width and form of the spectrum data may be obtained of nuclear positions. Hence, T2 determines the width of the resonance line, but has no correspondence with the saturation or the overall degree of occupation of the nuclear energy levels, like Ti has. T2 is always less than or equal to Ti (see Table 12.6). 

Figure 5 NMR titration of the pentacyclic acridinium cation RHPS4 (1) with the intermolecular quadruplex d(TTAGGT)4 monitoring the changes to the imino proton shifts and line widths of the three core G-tetrads, demonstrating fast-exchange characteristics as the signals broaden and then sharpen as the binding sites at the ApG and GpT steps are saturated (Adapted from ref 48).

Variable power measurements elucidate the saturation behavior of the nuclei. At low powers the NMR signal amplitude increases, and the line width remains unchanged with increasing rf power. At high powers saturation occurs, the resonant line broadens, and finally it decreases in amplitude with increasing rf power. Relaxation times may be eom-puted from saturation data (12). 

Viscosity-induced resonance broadening. Syn. viscosity broadening. The increase in the line width of peaks in a spectrum caused by the decrease in theTj relaxation time that results from a slowing of the molecular tumbling rate. Saturated solutions and solutions at a temperature Just above their freezing point often show this broadening behavior. 

Nuclear magnetic relaxation rates have been used to investigate the coordination number. In an investigation of the line-width broadening of La in various perchlorate solutions, Nakamura and Kawamura (1971) attributed the decreases in the values of (Av is the relaxation rate and is the relative viscosity) to a possible equilibrium between the nonahydrates and octahydrates for lanthanum ion. This conclusion was disputed by Reuben (1975) who proposed that this apparent anomaly reflected an erroneous estimate of the corrections of the linewidths for peaks due to the effect of the finite modulation amplitude and/or of partial saturation. Measurement of the transverse relaxation rates by the pulse method gave results consistent with a constant hydration number for lanthanum ion (Reuben 1975). 

Line-width The amplitude of an ESR 1st derivative line is inversely proportional to the line-width squared at a fixed concentration of free radicals. A narrow line-width is therefore desirable. The anisotropy of the g-factor and/or the hyperfine coupling causes line broadenings in several of the commonly used dosimeter materials, e.g. alanine and Li-formate. The line-width also tends to increase at microwave saturation, which is an additional reason for not increasing the power excessively. In practice the signal of an ESR-dosimeter may be distributed over several hyperfine lines, causing loss of sensitivity. For alanine five lines are present (Fig. 9.3). 

The spin-lattice relaxation, with a characteristic time Ti, is responsible for maintaining the population difference between levels, N and N+. The spin-spin relaxation time T2 reflects the lifetime of the excited state and its effect on the line width. If the electron-spin relaxation rate is too rapid, the lifetime of the excited state is short and the EPR spectrum becomes broadened. At high temperatures the spectrum may become too broad for detection, hence the use of cryogenic temperatures for some transition ions. However, if the spin-lattice relaxation is too slow, the population difference N - N+ cannot be maintained, and the amplitude of the signal is attenuated, a situation known as microwave power saturation. Electron-spin relaxation times may be estimated by measuring the amplitude of the signal as a function of applied microwave power. 

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