Low-temperature limit of the rate of propagation of chains in the hydrobromination of ethylene

The second (after the polymerization of formaldehyde) case of the low-temperature limit of the rate of elementary acts of propagation of chains in solid phase chemical chain reactions was found by the example of hydrobromination of ethylene.The average time of the development of new link of chain (τ〇) was determined by the method of differential diathermic calorimetric between 90 and 30 K. From 90 to 70 K this time increases in accordance with the Arrhenius law (E 〜 4 kCal/Mole), while at lower temperatures τ 〇 reaches gradually the plateau value [math] 〜 0, 1 sec, and the chain length is ν 〜 800 at 40 K. The existence of long chains and the appearance of the low-temperature limit of the rate of their propagation speaks in favor of tunnel mechanism of hydrobromination of ethylene at sufficiently low temperatures