Collision complex formation in the reactions of formyl radicals with nitric oxide and oxygen

摘要

The laser photolysis/resonance absorption technique has been used to measure absolute rate constants for the reactions of HCO and DCO with NO and O2at 295 K. The values of (1.26plusmn;0.2)times;10minus;11and (4.65plusmn;0.6)times;10minus;12cm3thinsp;moleculeminus;1thinsp;sminus;1for the reactions of HCO with NO and O2, respectively, are in good agreement with previously reported values. Deuterium substitution was found toincreasethe rate constants by 25percnt; and 10percnt; in reactions with NO and O2, respectively. These results are not explained within the framework of a direct hydrogen transfer mechanism and suggest that collision complexes are formed in both reactions. Simple RRKM calculations for a complex with a lifetime long compared to vibrational energy redistribution times semiquantitatively reproduce the experimental isotope effects, as well as the experimentally observed decreases in rate constant which result from vibrational excitation of the HCO or from an increase in temperature.