15min:
INVESTIGATION OF NUCLEAR SPIN CONVERSION OF METHANE IN SOLID HYDROGEN.

MIZUHO FUSHITANI AND TAKAMASA MOMOSE, Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.

We have studied nuclear spin conversion of CH4 and CD4 trapped in solid H2 and solid D2 by Fourier-transform infrared spectroscopy. It has been shown that the rotational quantum number J of methane is still a good quantum number in solid hydrogen. The effective rotational constant has been found to be about 90 % of the gas phase value. The vibration-rotation absorption of both CH4 and CD4 exhibited time-dependent intensity changes at liquid He temperatures. These changes are interpreted to be a result of the I=1 rightarrow I=2 nuclear spin conversion which accompanies the J=1 rightarrow J=0 rotational relaxation. The conversion rate is on the order of 10-3 min-1, but the rate depends on the temperature of the crystal. Mechanisms of the nuclear spin conversion in solid hydrogen will be discussed.