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Abstract

The spin relaxation time, T₁, has been measured at low densities in normal H₂ at 77°K, 196°K, 298°K and 392°K as a function of density using a 96 mHz pulsed N.M.R. spectrometer and a T₁ minimum obtained. The data at 77°K, where only the J=1 rotational state is populated, is fit by the conventional theories, but the results at higher temperatures are not explained by the generalization of the Bloom-Oppenheim⁽⁶⁾ theory. T₁ was also measured as a function of density for a mixture of 54.5% He in at 298°K in an effort to investigate the role of transitions between J states in the relaxation process. The spin relaxation time T₁ was also measured in HD as a function of density in the region of the T₁ minimum at 196°K and 298°K. Since the most recent theory has not been extended to a system of several populated J levels the results are rather inconclusive. T₁ was also measured in CH₄ as a function of density in the region of the T₁ minimum at 196°K and 298°K and information about the rotational coupling constants obtained. From these results it is concluded that measurements of T₁ as a function of density is very useful in testing theories of relaxation and obtaining information on the rotational coupling constants for polyatomic molecules.