Study of the reactions N+2+2N2→N+4+N2 and O+2+2O2→O+4+O2 from 20 to 160 K by the CRESU technique

Rate coefficients k1 and k2 have been determined for the association reaction N+2+2 N2→k1N+4+N2 and O+2+2 O2→k2O+4+O2 in the temperature range 20–160 K, using a supersonic jet apparatus (CRESU), which is described in detail. For the highest temperatures where other measurements exist, the measured values of the rate coefficients are in excellent agreement with previous measurements. The temperature dependence of k1 can be represented by a power law of the form k1=6.0×10−29 (300/T)1.85 from 20 K to higher temperatures. For k2, only lower limits for 20 and 45 K are reported but the present data do not confirm the existence of a maximum in k2 as suggested by other authors. These results are examined in the light of recent theoretical arguments.