This paper presents a study of coherent dynamic nuclear polarization (DNP) using frequency swept pulses at 94 GHz which optimize the polarization transfer efficiency. Accordingly, an enhancement ε ∼ 496 was observed using 10 mM trityl-OX063 as the polarizing agent in a standard 6:3:1 d 8 -glycerol/D 2 O/H 2 O glassing matrix at 70 K. At present, this is the largest DNP enhancement reported at this microwave frequency and temperature. Furthermore, the frequency swept pulses enhance the nuclear magnetic resonance (NMR) signal and reduce the recycle delay, accelerating the NMR signal acquisition.

This paper presents a study of coherent dynamic nuclear polarization (DNP) using frequency swept pulses at 94 GHz which optimize the polarization transfer efficiency. Accordingly, an enhancement ℇ∼496 was observed using 10mM trityl-OX063 as the polarizing agent in a standard d8-glycerol:D2O:H2O :: 6:3:1 glassing matrix at 70K. At present this is the largest DNP enhancement reported at this microwave frequency and temperature. Furthermore, the frequency swept pulses enhance the nuclear magnetic resonance (NMR) signal and reduce the recycle delay, accelerating the NMR signal acquisition.

We propose a new mechanism for dynamic nuclear polarization that is different from the well-known Overhauser effect, solid effect, cross effect and thermal mixing processes. In particular, we discovered that the evolution of the density matrix with the simple Hamiltonian of a coupled electron-nuclear spin pair with weak microwave irradiation yields a nuclear polarization enhancement when irradiating near the electron Larmor frequency. We denote the mechanism as Resonant Mixing (RM). We believe that this mechanism is responsible for the observed dispersive shaped DNP field profile for trityl samples near the electron paramagnetic resonance center. This new effect is due to mixing of states by the microwave field together with the electron-nuclear coupling, and involves the same interactions as the SE. However, the SE is optimal when the microwave field is off-resonance, whereas RM is optimal when the microwave field is on-resonance.