NMR studies of single crystals of H2: II. The spectrum of isolated ortho-H2 pairs

Abstract

The NMR spectrum of isolated ortho-H2 pairs has been measured on two single crystals of H2 with ortho concentrations below about 2%. The experiments were carried out over a temperature range between 0.025 and 1 K, and spectra were recorded with the magnetic field applied in a number of directions. Extending the previous analysis of the spectrum for isolated ortho-H2 to the present data led to the determination of the crystal orientation. The complicated pair spectrum includes the signals from the nine nonequivalent pair orientations in the crystal and is a function of the two lowest rotational states. These states are split by an energy δ, which is different for the pairs with axis respectively in and out of the basal plane of the crystal (denoted IP and OP), namely % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4baFfea0dXde9vqpa0lb9% cq0dXdb9IqFHe9FjuP0-iq0dXdbba9pe0lb9hs0dXda91qaq-xfr-x% fj-hmeGabaqaciGacaGaaeqabaWaaeaaeaaakeaacqqHuoarcaGGOa% Gaam4taiaadcfacaGGPaGaai4laiaadUgadaWgaaWcbaGaamOqaaqa% baGccqWIdjYocaaI2aGaaGinaiaad2gacaWGlbaaaa!3DD4!\[\Delta (OP)/k_B \simeq 64mK\] and % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4baFfea0dXde9vqpa0lb9% cq0dXdb9IqFHe9FjuP0-iq0dXdbba9pe0lb9hs0dXda91qaq-xfr-x% fj-hmeGabaqaciGacaGaaeqabaWaaeaaeaaakeaacqqHuoarcaGGOa% GaamysaiaadcfacaGGPaGaai4laiaadUgadaWgaaWcbaGaamOqaaqa% baGccqGH8aapcaaI1aGaaeiiaiaad2gacaWGlbaaaa!3D85!\[\Delta (IP)/k_B < 5{\rm{ }}mK\].