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Science 4 December 1987:
Vol. 238. no. 4832, pp. 1393 - 1394
DOI: 10.1126/science.238.4832.1393
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Articles

Rotation and Solvation of Ammonium Ion

CHARLES L. PERRIN 1 and ROBERT K. GIPE 1

1 Department of Chemistry, D-006, University of California, San Diego, La Jolla, CA 92093.

From nitrogen-15 spin-lattice relaxation times and nuclear Overhauser enhancements, the rotational correlation time Tc for 15NH4+ was determined in a series of solvents. Values of Tc range from 0.46 to 20 picoseconds. The solvent dependence of Tc cannot be explained in terms of solvent polarity, molecular dipole moment, solvent basicity, solvent dielectric relaxation, or solvent viscosity. The rapid rotation and the variation with solvent can be accounted for by a model that involves hydrogen bonding of an NH proton to more than one solvent molecule in a disordered solvation environment.

Submitted on July 20, 1987
Accepted on October 14, 1987

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Science. ISSN 0036-8075 (print), 1095-9203 (online)