Spin-lattice relaxation times of H-2 and D-2 in aqueous solutions

The H-1 and H-2 NMR spectra of hydrogen (H-2) and deuterium (D-2) gas dissolved in aqueous media were recorded over a range of temperatures. In D2O/1 M DCl, the H-1(2) and HOD peaks were 278 Hz apart at 283 K, and 64 Hz apart at 323 K; this enabled the measurement of T-1 by the inversion-recovery pulse sequence. The T-1 value ranged from 1.84 s at 283 K to 2.12 s at 323 K; the value was proportional to temperature with a low thermal coefficient, and Arrhenius analysis yielded a T-1 activation energy of only -2.68 +/- 0.3 kJ mol(-1), The relaxation rate could be accounted for by both spin-rotation and dipolar mechanisms, which are inextricably linked, and apply to ortho-H-1(2) alone, The H-2 NMR spectrum of D-2 in H2O/1 M HCl had a resonance 28 Hz to low frequency of HOD. The relaxation behavior at 298 K was biexponential with T-1 values of 2.0 +/- 1.2 and 39.1 +/- 5.4 s for the para and ortho species, respectively. (C) 1996 Academic Press, Inc.