Nuclear Spin Relaxation and Double Resonance in HD Gas

Nuclear magnetic double-resonance experiments were performed on a gaseous sample containing a mixture of HD and C${\mathrm{O}}_2$ at high pressure by observing the spin-spin multiplet in the proton-resonance spectrum and irradiating either the deuteron transitions or some of the proton transitions. The spectra show features arising from spin relaxation in HD. These features are analyzed by using the density-matrix theory of double resonance, assuming "strong"- and "weak"-collision models for the system. The equation of motion of the spin density matrix is exactly of the same form for both collision models, the only distinction coming from the dependence of the correlation times on the transformation properties of the lattice operators and on the quantum numbers characterizing the lattice states. The results of the analysis of HD double-resonance spectra indicate that the collisions in this case are "strong." The cross products between lattice terms which transform identically but belong to two different relaxation mechanisms make significant contributions to some of the correlation functions involved and thereby affect the final results.