Knowledge Bank

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.