Nuclear Spin Relaxation of Matrix-Isolated Hydrogen Deuterium

357MHz and 55MHz proton and 55MHz deuteron nuclear spin-lattice relaxations and spin-spin relaxations of HD dilute in solid argon have been studied as function of temperature and of HD concentration, respectively. The T_1 results show two temperature regimes over a temperature range 9.9K ~ 65K. Below 45K, the spin-lattice relaxation time varies with temperature but is independent of HD concentration. The spin-lattice relaxation arises from phonon driven molecular reorientations of J = 1 HD molecules. Dilute HD molecules experience a static electric field gradient smaller than those seen by ortho-H_2 and para -D_2 in solid argon. Above 45K, proton T_1 of HD in solid argon was measured as a function of HD concentration at 60K, over a HD(J = 1) concentration range from 10 ppm to 265ppm. A T_1 minimum with C ^{+/-5/3} slopes was observed. The warm sample T_1 relaxation appears to be induced by EQQ intermolecular interactions, which appear as HD moves due to the argon lattice self -diffusion. The proton T_2 of HD in solid argon increases with temperature and reflects motional narrowing.