Solid H2 and D2: Remarkable differences in some NMR properties

Separation of the ortho and para NMR signals in solid deuterium via DQ filtering

Double quantum (DQ) filtering is shown to lead to an effective separation of the NMR signals from the para (I = 1) and ortho (I = 2) molecules in solid deuterium. The separation is achieved by the pulse sequence 90(φ)( degrees )-t(pr)-90(φ)( degrees )-t(ev)-90(x)( degrees )-t, where the phase-cycled first two pulses create the DQ coherence. Two components are observed after the third pulse; the para signal shows the maximum at a short time t while the ortho signal reaches the maximum at a longer t. The observed signal can be expressed as (1/2) summation operator(I) [F(I)(t(pr) - t) - F(I)(t(pr) + t)], where F(I)(t) is a proper fitting function for the free induction signal of the para and ortho molecules (with I = 1 or 2, respectively). Numerical fits to experimental data at 4.2 and 2 K show that this method can be used to determine the ratio F(1)(0)/F(2)(0) and thus, because the initial value F(I)(0) is proportional to the respective magnetization before the pulse sequence, the ortho and para concentrations in solid deuterium. Copyright 2000 Academic Press.