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Fluid Structures ofCO 2 andCO 2 –CH 4 Mixture at Supercritical Fluid and Liquid Densities by Nuclear Spin–Lattice Relaxation Measurements
Author(s) -
Bai Shi,
Mayne Charles L.,
Pugmire Ronald J.,
Grant David M.
Publication year - 1996
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/(sici)1097-458x(199606)34:6<479::aid-omr905>3.0.co;2-h
Subject(s) - supercritical fluid , chemistry , intermolecular force , relaxation (psychology) , anisotropy , chemical physics , dipole , molecule , organic chemistry , psychology , social psychology , physics , quantum mechanics
13 C nuclear relaxation times were measured by a high‐pressure sapphire NMR cell for neat CO 2 and a CO 2 –CH 4 mixture over a wide range that covers gas, liquid and supercritical densities. The nuclear spin–lattice relaxation times at liquid and supercritical densities for the CO 2 –CH 4 mixture were obtained for the first time. Although the spin–rotation interactions still dominate the spin–lattice relaxation processes in CH 4 , the intramolecular dipolar interaction contributes approximately 5% to the overall relaxation rates at liquid densities for this mixture. The chemical shift anisotropy and the intermolecular contributions to the relaxation rates of CO 2 were experimentally determined to be negligible. A movable wall cell model was modified and used to relate the relaxation time data to the fluid structures of the first solvation shell around the central molecules in the liquid and supercritical fluid states. The coordination number in the first shell was found to be 12 for both the neat CO 2 and CO 2 –CH 4 mixture at liquid and supercritical fluid densities.