Abstract
The gaseous diffusion coefficients of methyl bromide (CH3Br ) and methyl iodide (CH3I) into dry air, nitrogen and oxygen have been measured in the temperature range 303-453 K and at atmospheric pressure by the use of the Taylor dispersion method. Both for methyl bromide and methyl iodide, the diffusion coefficients do not vary in practice on substituting pure nitrogen or oxygen for dry air. The diffusion coefficients for methyl iodide are systematically smaller than those for methyl bromide by about 11%. For the methyl iodide-oxygen system, the effect of the thermal decomposition of methyl iodide has been observed at 453 K. The present results can be reproduced well by the functional form D = ATB, where D (cm2s-1) is the diffusion coefficient at 101 325 Pa (1 atm) and T (K) is the absolute temperature. The constants A and B are as follows: methyl bromide-(air, nitrogen, oxygen), A = 5.57×10-6, B = 1.76; methyl iodide-(air, nitrogen, oxygen), A = 5.26×10-6, B = 1.75.
