Diffusion-broadened velocity spectra of convection in variable-temperature BP-LED experiments

When NMR diffusion experiments are performed at temperatures different from ambient temperature, temperature gradients due to probe design can cause thermal convection and therefore significantly affect the signal amplitude. Fourier transformation of the signal amplitude gives rise to a diffusion-broadened velocity spectrum, which contains information about the convection velocity. It is shown that when the diffusion broadening factor is smaller than the maximum velocity, the broadening has little effect on the determination of the maximum velocity. Thus, convection velocity can be determined in the presence of diffusion. (C) 2001 Academic Press.