C-13 AND H-1 SPIN RELAXATION IN CH4 IN THE GAS-PHASE

The dominance of the spin-rotation mechanism in the relaxation of both the C-13 and the H-1 nuclear spins in (CH4)-C-13 in various buffer gases has been established. Cross sections for changes in the rotational angular momentum vector of CH4 molecules in collisions with various molecules have been obtained as a function of temperature from the measured spin relaxation times of C-13 or H-1 or both. At 300 K these cross sections are 18.8 +/- 0.5 angstrom-2 (CH4-CH4), 16.3 +/- 0.3 angstrom-2 (CH4-N2), 15.8 +/- 0.2 angstrom-2 (CH4-CO), 24 +/- 1 angstrom-2 (CH4-CO2), 15 +/- 1 angstrom-2 (CH4-Ar), 18.3 +/- 0.6 angstrom-2 (CH4-Kr), 22.4 +/- 0.2 angstrom-2 (CH4-Xe), 24 +/- 1 angstrom-2 (CH4-HCl), 25 +/- 1 angstrom-2 (CH4-CF4), 34.5 +/- 1.1 angstrom-2 (CH4-SF6), and 24.0 +/- 0.8 angstrom-2 (CH4-SiH4).