Abstract
Measurements of the proton relaxation times in water as a function of pH were made. The transverse relaxation time T/sub 2/ was measured by the spin-echo method. The longitudinal relaxation time T/sub 1/ was measured by ihe 18O deg to 90 deg pulse scheme. The water used was doubly distilled, but not degassed. Its pH was adjusted by the addition of HCl in the acid range and NaOH in the basic range, and measured with a glass electrode. It appears that the observed dependence of T/sub 2/ on pH is not due to the presence of Na/sup +/ or Cl/sup -/ ions. The fact that T/su 2/ is appreciably shorter than T/sub 1/ shows that part of the relaxation is caused by a slow mechanism, i.e., one characterized by a correlation time longer than the Larmor period. It is proposed that in the central pH range, the periinent mechanism is the breaking and reforming of hydrogen bonds between water molecules. There is strong evidence that the hydrogen bonding causes a chemical shift of the proton resonance of the order of 100 cps (at 30 Mcps). (A.C.)
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