Carr-Purcell technique

In earlier studies on diffusion of PDMS, the Carr-Purcell technique was used with magnetic field gradients present at all times (SFG NMR). The measurement of small diffusion coefficients (e.g., in polymers) requires strong gradients which means that as gradient strength is increased wider resonance lines and narrower echo envelopes will be... 

Pulse techniques have been used by Powles et al (1960, 1962) to measure temperature dependence of nuclear spin-spin coupling in molecules such as methanol and acetaldehyde, which have steady-state spectra approximating to an AX3 case (Pople etal. 1959). Hahn and Maxwell (1951, 1952) showed that modulations of echo amplitudes could be explained on the basis of scalar couplings. In the limit of weak coupling the formulae are simplified and the chemical shift modulation disappears. In a Carr-Purcell experiment the amplitude of the %th echo E (t) in an AX3 case can be shown to be... 

The technique for obtaining reliable values of Tj involves the application of fmlher short rf-pulses to the nuclear spin system such that spin echoes are obtained. In this review, we shall discuss briefly the Carr-Purcell pulse sequence for producing spin echoes with the modification introduced by Maiboom and Gill . After the initial 90° pulse along the x-direction in the rotating frame (cf. first section of this chapter), pulses with cc = = 180° are applied along the... 

The quadrupolar Carr-Purcell Meiboom-Gill technique... 

According to Wiench et al. (2008), a remarkable enhancement of sensitivity can be achieved in Si solid-state NMR by applying the Carr-Purcell-Meiboom-Gill (CPMG) train of rotor-synchronized Ji pulses during the detection of Si magnetization. They used several one- and two-dimensional (ID and 2D) techniques to demonstrate the capabilities of this approach. Examples include ID Si X CPMAS spectra and 2D Si X HETCOR spectra of mesoporous silicas, zeolites, and minerals,... 

Spin-spin relaxation times have been determined by the Carr-Purcell-Meiboom-Gill 90 -[(180 )j-echo] sequenze at a frequenzy of 20 MHz using a Bruker Minispec pclOO at a field strength of 0.47 T. The operational temperature was 40 °C in order to prevent temperature changes due to external influences. All samples were stored at 40°C. The magnetization curve was analyzed using a monoexponential fit. A multiexponential technique yielded no perceivable improvement of the quality of the fit. 

It has been demonstrated by Wiench et al that in the case of Si-Si doublequantum techniques, the well known Carr-Purcell-Meiboom-Gill(CPMG) train of rotor-synchronised n pulses during the detection of silicon magnetization can be exploited to measure homonuclear Vsi-si couplings. 

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