Spectroscopic determination of interconversion rates among three nuclear spin isomers of methane in crystalline II

Sugimoto, Takeru*; Nasu, Hirokazu*; Arakawa, Ichiro*; Yamakawa, Koichiro   

We measured infrared absorption spectra of crystalline II of methane and succeeded in detecting a prominent Q(2) peak by rapid cooling after annealing as well as previously reported rovibrational and librational-vibrational peaks. The integral intensities of the R(0), R(1), and Q(2) peaks were found to show biexponential dependence on time. This clearly demonstrates the interconversion among the three nuclear-spin isomers occupying low-lying rotational levels.