The recombination of atoms II. Causes of variation in the observed rate constant for iodine atoms

Abstract A re-investigation of the recombination of iodine atoms in presence of the inert gases over a wider range of experimental conditions has shown that the simple termolecular rate law — d(I)/dt = k(I)2 (M) is not obeyed. For each of the inert gases k, the experimentally determined termolecular rate constant, increases with the ratio (I2)/(M), where (I2) and (M) are the concentrations of iodine m olecules and inert gas molecules respectively. The dependence of k on (I2)/(M) was obscured in previous work by the fact that a thermal effect, which results in a lowering of the apparent value of k as recombination proceeds, increases as (I2)/(M) increases and compensated for the real increase in k with (I2)/(M). Except at low (I2)/(M) values, k is a linear function of (I2)/(M), the gradient being the same for all five inert gases. A rapid termolecular reaction I+I+I2=I2+I'3 with a rate constant k = 470 x 10-32 ml.2 mol.-2 s-1 is postulated to explain the linear relationships. B y extrapolation the values of kM the third-order rate constants for the five inert gases are M 1032kM (ml.2 mol.-2 s-1) He Ne A Kr Xe 0.67 0.92 1.84 2.25 2.99