Adiabatic Solid Effect

Tan, Kong Ooi, Ralph T. Weber, Thach V. Can, and Robert G. Griffin. “Adiabatic Solid Effect.” The Journal of Physical Chemistry Letters, April 20, 2020, 3416–21.

The solid effect (SE) is a two spin dynamic nuclear polarization (DNP) mechanism that enhances the sensitivity in NMR experiments by irradiation of the electron-nuclear spin transitions with continuous wave (CW) microwaves at 𝜔0S ± 𝜔0I, where 𝜔0S and 𝜔0I are electron and nuclear Larmor frequencies, respectively. Using trityl (OX063), dispersed in a 60/40 glycerol/water mixture at 80 K, as a polarizing agent, we show here that application of a chirped microwave pulse, with a bandwidth comparable to the EPR linewidth applied at the SE matching condition, improves the enhancement by a factor of 2.4 over the CW method. Furthermore, the chirped pulse yields an enhancement that is ~20 % larger than obtained with the ramped-amplitude NOVEL (RA-NOVEL), which to date has achieved the largest enhancements in time domain DNP experiments. Numerical simulations suggest that the spins follow an adiabatic trajectory during the polarization transfer; hence, we denote this sequence as an adiabatic solid effect (ASE). We foresee that ASE will be a practical pulsed DNP experiment to be implemented at higher static magnetic fields due to moderate power requirement. In particular, the ASE uses only 13 % of the maximum microwave power required for RA-NOVEL.

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