title: Nuclear spin conversion of methane in solid parahydrogen.
abstract: The nuclear spin conversion of CH(4) and CD(4) isolated in solid parahydrogen was investigated by high resolution Fourier transform infrared spectroscopy. From the analysis of the temporal changes of rovibrational absorption spectra, the nuclear spin conversion rates associated with the rotational relaxation from the J=1 state to the J=0 state for both species were determined at temperatures between 1 and 6 K. The conversion rate of CD(4) was found to be 2-100 times faster than that of CH(4) in this temperature range. The faster conversion in CD(4) is attributed to the quadrupole interaction of D atoms in CD(4), while the conversion in CH(4) takes place mainly through the nuclear spin-nuclear spin interaction. The conversion rates depend on crystal temperature strongly above 3.5 K for CH(4) and above 2 K for CD(4), while the rates were almost constant below these temperatures. The temperature dependence indicates that the one-phonon process is dominant at low temperatures, while two-phonon processes become important at higher temperatures as a cause of the nuclear spin conversion.
authors: Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto, Japan.
authors: Yuki
authors: Y
authors: Miyamoto
authors: Mizuho
authors: M
authors: Fushitani
authors: Daisuke
authors: D
authors: Ando
authors: Takamasa
authors: T
authors: Momose