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Y. MIYAMOTO, M. FUSHITANI, H. HOSHINA AND T. MOMOSE, Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
Because of weak nuclear magnetic interactions, conversion between different nuclear spin states is a very slow process in the gas phase. On the contrary, the conversion in condensed phases is known to be quite fast. However, mechanism of the fast conversion in condensed phases has not been well understood yet. Last year at this meeting, we reported the nuclear spin conversion of CH4 imbedded in solid parahydrogen. We showed that the nuclear spin conversion in the solid is greatly accelerated by lattice vibrations of the crystal. Here, we report the nuclear spin conversion of CD4 imbedded in parahydrogen solid. The rate of the nuclear spin conversion was obtained by the temporal change of rotation-vibration transition intensities of CD4. Despite the small nuclear spin-nuclear spin coupling constant of CD4 compared with that of CH4, the conversion rate of CD4 is found to be more than two times larger than that of CH4 at the same temperature. In addition, the conversion of CD4 shows stronger temperature dependence than that of CH4. The difference of the nuclear spin conversion processes between CD4 and CH4 will be discussed.