The free radical oxidation of CH 2O in the presence of NO 2 and NO

Abstract

NO 2 was photolyzed at 366 nm and 296 K in the presence of CH 2O and O 2 and in some runs with added NO or N 2. The measured products were CO, CO 2 and HCOOH. H 2 and N 2O were not produced. Both the CO and the CO 2 were produced in a linear fashion with irradiation time, but the HCOOH grew after a marked induction period. From the CO 2 quantum yields at high [O 2]/[NO 2] ratios an upper limiting value of 0.16 ± 0.02 was found for k 3b/ k 3 where reactions (3a) and (3b) are ▪ ▪ This is lower than the value of approximately 0.30 reported for k 3b/ k 3 by Chang and Barker. From the CO and CO 2 yields the competition for HCO between O 2 and NO 2 could be measured. ▪ ▪ The ratio k 9/ k 7a was found to be 0.21 ± 0.07 and was independent of pressure. The analysis required knowledge of some other rate coefficients. If those rate coefficients are completely in error, k 9/ k 7a could be as high as 0.63. With the literature value of 5.6 × 10 −12 cm 3 s −1 for k 9, the best value for k 7a is (2.7 ± 0.9) × 10 −11 cm 3 s −1 with a lower limiting value of (8.9 ± 3.0) × 10 −12 cm 3 s −1. Information was also obtained on the reaction of HO 2 with CH 2O which produces HCOOH. An approximate value of (1.4 – 3.2) × 10 −13 cm 3 s −1 was found for the rate coefficient for this reaction which is about 14 – 32 times greater than the estimate of Su et al.