Nuclear spin conversion of methane in condensed layers at low temperatures

Yamakawa, Koichiro   ; Sugimoto, Takeru*

Methane has three kinds of nuclear spin isomers: ortho (I = 1), meta (I = 2), and para (I = 0). Methane is a spherical top molecule, and its rotational energy is dependent on the rotational quantum number J. The J = 0 (J = 1) level is occupied only by the meta (ortho) isomer while the ortho and para states are degenerate at the J = 2 level. Because of this degeneracy, the conversion between ortho and para proceeds considerably fast, with the result that only the ortho-meta conversion has been observed in matrices of rare gases and para hydrogen. On the other hand, the nuclear spin conversion between three kinds of the isomers has recently been observed in the lower-temperature phase of crystalline methane. In this presentation, the infrared spectroscopic study on the ortho-meta-para conversion in crystalline methane is demonstrated, comparing with previous matrix-isolation studies.