The rate of quenching of CO2(010) by O(3p) has been measured at room temperature by a temperature-jump method. The rate constant value obtained is in good agreement with a previous room-temperature measurement based on steady-state analysis of a hollow-cathode discharge in CO2. The results of fitting the room-temperature result to trajectory calculations with a curve-crossing (Nikitin) energytransfer mechanism lead to the conclusion that the quenching rate constant should increase only slowly with increasing temperature.

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A new variant of the temperature-jump method has been used to measure the rate of quenching of CO2(O10) by O(,P). The value found for the rate constant at room temperature is 1.2 & 0.2 x lo-'' cm3 molecule-' s-', in good agreement with a previous laboratory study. Our trajectory calculations show that such a large value of the room-temperature rate constant is not explicable in terms of an impulsive (Landau-Teller) mechanism but can be understood in terms of a curve-crossing (Nikitin) mechanism. However, the impulsive mechanism is still required to account for the strong temperature dependence of previous high-temperature, shock-tube results.Preliminary measurements of the rate of quenching of N,O(OlO) by O(3P) give a rate constant value similar to that found for CO,, which implies that formation of a bound triplet state of CO, plays very little part in the quenching process for CO2(O10).

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