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Issue 18, 2012
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Theory of the Overhauser effect in the pulsed mode of EPR pumping: exploiting the advantages of coherent electron spin motion

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Abstract

A theoretical approach is proposed to describe Overhauser-type Dynamic Nuclear Polarization (DNP) for pulsed EPR pumping by application of a train of short pulses with a duration on the nanosecond time scale. We obtained an elegant general expression for the NMR enhancement provided by the DNP effect. The expression for the enhancement is similar to that known for cw-pumping except for the saturation factor, which is re-defined as the deviation of the electron spin magnetization from its equilibrium value averaged over the cycle of the pulse sequence. It is shown that one can achieve the maximal theoretically allowed NMR enhancement for pulsed pumping even when the duty cycle of pumping is low. This becomes possible because coherent motion of the electron spins in the B1-field is exploited, a key feature of the pulsed DNP experiment also enabling optimization of the achievable NMR enhancement. The dependence of the effect on the duty cycle, pulse duration and electron spin relaxation times has been studied in detail. Once the lines in the EPR spectrum are inhomogeneously broadened, higher DNP effects are expected in the pulsed pumping mode than in the cw-mode for the same total power of microwave irradiation. The theoretical results are in good agreement with experimental data obtained for the pumping frequencies of 300 MHz and 1.4 GHz.

Graphical abstract: Theory of the Overhauser effect in the pulsed mode of EPR pumping: exploiting the advantages of coherent electron spin motion

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Publication details

The article was received on 06 Dec 2011, accepted on 05 Mar 2012 and first published on 05 Mar 2012


Article type: Paper
DOI: 10.1039/C2CP23896A
Citation: Phys. Chem. Chem. Phys., 2012,14, 6459-6468

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    Theory of the Overhauser effect in the pulsed mode of EPR pumping: exploiting the advantages of coherent electron spin motion

    E. A. Nasibulov, K. L. Ivanov, A. V. Yurkovskaya and H. Vieth, Phys. Chem. Chem. Phys., 2012, 14, 6459
    DOI: 10.1039/C2CP23896A

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