Studies in energy transfer I. The combination of iodine atoms

Abstract

An experimental study has been made of the velocity of combination of iodine atoms in the presence of a number of added gases in order to investigate the factors influencing energy transfer. The reaction cell, containing iodine at a pressure of 0.097 mm Hg and a known pressure of third body, is irradiated with a flash from a discharge tube. The concentration of iodine atoms as recombination proceeds is determined by measuring the light absorption of the system with a photomultiplier tube. The reaction is second order with respect to the concentration of iodine atoms, and first order with respect to the third body. The third-order rate constants vary from 0.97 x 10-32mol.-2cm6s-1when helium is added to 224 x 10-32mol-2cm6s-1for mesitylene. The velocity of combination at 127° C has been found to be approximately 0.4 time the velocity at 20° C for six different additives. This factor seems to be independent of the nature of the additive. The efficiencies of the different additives is primarily determined by the magnitudes of their intermolecular force fields, which are reflected in their boiling-points and critical temperatures.