Dynamic Nuclear Polarization Studies of Charred Carbohydrates

Abstract

The dynamic enhancement of proton spin polarization by pumping on ``forbidden'' electron‐nuclear transitions is studied as a function of microwave power, O2 pressure, and magnetic field for a pair of low‐temperature paramagnetic sucrose chars. The dependence of the electron spin‐lattice relaxation time on O2 pressure is obtained for both samples. Comparison of the enhancement for a 405°C char with theory indicates that the electron spin resonance line is inhomogeneously broadened, and yields absolute values for the spin‐spin and spin‐lattice relaxation times of the spin packets. No definite fit could be made to the 605°C char data. The difference between the magnetic fields for maximum positive and negative polarization enhancement is anomalously small for the 405°C char.