A proton T1-nuclear magnetic resonance dispersion study of water motion in snowflakes and hexagonal ice

Abstract

ABSTRACTSnowflakes and ordinary hexagonal ice were studied measuring water proton spin–lattice relaxation rate -nuclear magnetic resonance dispersion (NMRD) profiles at proton Larmor frequencies ranging from 1 to 30 MHz and at different temperatures ranging from C to C. The spin–spin relaxation rate 1/ was determined at a single Larmor frequency of MHz. The high-field wing of the proton -NMRD profile was characterised by two parameters: a correlation time which described the dipole–dipole spectral density, and the relaxation rate at low fields which was determined from . The correlation time depended on the dynamic model used. A rotation diffusion model yield approximatively s at C to about s at C, whereas for a more realistic six-site discrete exchange model, the correlation times decreased slightly to about 80% for the same temperature interval. Proton dipole–dipole interactions were divided into intramolecular and intermolecular contributions where the intermolecular contribution was about 0.4–0.8 × the intramolecular contribution. It was not possible to discriminate between the dynamic models or to detect ice/water interface effects by comparing the NMRD data from snowflakes with ordinary hexagonal ice data.