Line width at half-height

Although this equation only applies when the coalescence point is reached, rate constants for the exchange between two or more exchanging sites are accessible by analysis of line widths at half height, Avip, and shift differences, Ar, in Hz. The comparison between the experimental spectrum and the spectrum calculated by use of a simulation package for line shapes provides the mechanism for determining the rate constant of exchange [161, 162]. 

The gas flow rates are adjusted to ensure a constant pressure inside the cell and to minimize degradation of the spectral resolution by the gas bubbles. Typical line-widths at half height are <4 Hz on NMR (200 MHz) and <2 Hz on (80.3 MHz). The probe fits into the room temperature shims of a wide-bore NMR magnet and the pressure and temperature range of the high pressure NMR flow are 0.1 to 20 MPa and -40 to 175 °C, respectively. 

Chemical shifts of bulk and coordinated water differ and as a result, the line width at half-height can be used to calculate the rate of chemical exchange. If reactions are slow, NMR methods can be used directly to determine reaction rates since one need only follow the isotopic enrichment of a complex. 

The natural line-width of the proton resonances is determined by the nuclear spin relaxation times. Nuclear relaxation in solutions of diamagnetic molecules comes mainly from intramolecular proton-proton dipolar coupling modulated by the rotational tumbling of the molecules, and will be discussed in more detail in section VII. Suffice it here to say that the line-width increases in general with increasing size of the molecule. For a small organic molecule a line-width at half height of the resonances of less than one cps would be expected, whereas the resonances... 

AH EPR line width between the points of maximum slope AH 1/2 EPR line width at half height... 

The broadening of the resonance band may be characterised by the line width at half height (ABy2) or by the second moment of the curve which is defined as... 

Correlated with the line width at half height is the spin-spin relaxation time T2. In case the line shape is Lorentzian, we get... 

It is customary to keep the frequency constant while the field B is varied. At the commonly used frequency of 9.5 GHz (known as X-band microwave radiation and thus giving rise to X-band spectra) resonance occurs at a magnetic field of 0.34 T. Disturbances again cause a band of finite width, characterised by the line width at half height (ABi/2) again dipole-dipole interactions of the spins is a reason of the width of the resonance lines. 

Characteristic of the order-disorder transition caused by this interaction is the so-called spin-spin relaxation time (T2), which is correlated with the line width at half height for a line of Lorentzian shape ... 

Intrinsic resolution, R, is defined by the minimum line width at half height, Avi/2, of the CoHft signal in a CDCI3 solution 60 to 80 Hz are typical values observed in lignin spectra, much higher than instrument specifications. 

The term the line width at half-height of the coalesced peak and is equal to... 

The temperature dependence of the NMR absorption in coals and pitches has been obtained by using a pulsed Fourier transform NMR spectrometer with a high-tempera-ture probe. With increasing temperature the value of the line width at half height of a brown coal decreases... 

Figure 3. Temperature dependence of the line width at half-height (A Hj ) during heating at 5 K min (O) Taiheiyo coal ( ) Yubarishinko coal (LJj P component of Yubarishinko coal 7 component of Yubarishinko coal ( + j...

Analyses of the -decoupled 13C NMR spectrum of the commercial sample of dibutyltin di-isooctylthioglycolate used in this study indicates that its thioglycolate precursor is produced from a mixture of C8 aliphatic alcohols and thioglycolic acid (HSCH2COOH). Consequently, the aliphatic portion of its 13C spectrum (0-60 ppm) is extremely complex. However, only one carbonyl carbon resonance is present (line width at half height = 4.7 Hz), and its chemical shift (173.9 ppm) is separated widely from those of the aliphatic carbons. The carbonyl group in these compounds apparently is not subject to the larger substituent effects well-documented for alkanes (II) and other classes of compounds. Thus, the carbonyl carbon resonance was used to monitor the reaction. 

The full line width at half-height, r, and 1.16 for Fe(i)S-C5H5)(CO)2SnMe3. 

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