Kinetics and Mechanism of the Photooxidation of Formaldehyde. 1. Flash Photolysis Study

Article abstract of DOI:10.1021/j100343a033

Transient species in the photooxidation of formaldehyde in air have been investigated by using the technique of flash photolysis kinetic spectroscopy.The absorption spectrum attributed to the HOCH2O2 radical was observed with a maximum near 230 nm.This radical is formed by the reaction HO2+HCHO<*>HOCH2O2 (1,-1).The rate constants were measured for the two reactions: k₁=7.7E-15*exp<(625+/-550)/T> cm³ molecule^-1 s^-1 and k_-1=2.0E12*exp<(-7000+/-2000)/T> s^-1.The equilibrium constant is K₁^*=3.85E-27*exp(7625/T) cm³ molecule^-1, which corresponds to a reaction enthalphy ΔH₁⁰=-16.25+/-0.30 kcal mol^-1,which is based on the K_p value and quantum calculations of ΔS₀⁰ and therefore determined accurately.Kinetic measurements performed under various experimental conditions allowed determinations of the rate constants for the reactions HO2+HOCH2O2<*>products (3) and 2HOCH2O2<*>>O2+CH2(OH)2+HCOOH (4b); k₃=5.6E-15*exp<(2300+/-1100)/T>; k_4b=5.65E-14*exp<(750+/-400)/T> cm³ molecule^-1 s^-1.The branching ratios for k₃ and k₄ were determined in separate experiments described in part 2 of this work.