Kinetics and Mechanism of the Photooxidation of Formaldehyde. 2. Molecular Modulation Studies.

Article abstract of DOI:10.1021/j100343a034

Transient species in the photooxidation of formaldehyde in air have been investigated by using the technique of modulated photolysis-long path kinetic spectroscopy.A transient absorption spectrum consisting of a broad band with a maximum near 230 nm was obseved, which is attributed to the HOCH2O2 radical formed by the reaction HO2+HCHO<*>HOCH2O2 (1).The equilibrium constant, K₁^* was estimated from these measurements of the HOCH2O2 radical together with measurements of HO2 obtained with diode laser infrared absorption spectroscopy:K₁^*=4.0(+4.0,-2.0)E-16 cm³ molecule^-1 at 298 K.Kinetic measurement of the two radicals allowed determination of the rate coefficients at 298 K for the following reactions: HOCH2+HO2<*>products (3), k₃=(1.2+/-0.3)E-11 cm³ molecule^-1 s^-1; 2HOCH2O2<*>HCOOH+CH2(OH)2+O2 (4b), k_4b=(5.6+/-2.8)E-13 cm³ molecule^-1 s^-1.The alternative pathway, 2HOCH2O2<*>2HOCH2O+O2 (4a), followed by HOCH2O+O2 leads to the chain generation of formic acid.The rate coefficient for reaction 4a, k_4a=(5.5+/-1.1)E-12 cm³ molecule^-1 s^-1, was determined from the yields of formic acid.