Direct measurements of the reaction H + CH₂O → H₂+ HCO behind shock waves by means of Vis–UV detection of formaldehyde

The combination of sensitive detection of formaldehyde by 174 nm absorption and use of ethyl iodide as a hydrogen atom source allowed direct measurements of the reaction H + CH 2 O → H 2 + HCO behind shock waves. The rate constant was determined for temperatures from 1510 to 1960 K to be k 2 = 6.6 × 10 14 exp(−40.6 kJ mol −1 / RT ) cm 3 mol −1 s −1 (Δ log k 2 = ± 0.22) Considering the low uncertainty in k 2 , which accounts both for experimental and mechanism‐induced contributions, this result supports the upper range of previously reported, largely scattered high temperature rate constants. Vis–UV light of 174 nm was generated by a microwave N 2 discharge lamp. At typical reflected shock wave conditions of 1750 K and 1.3 atm, as low as 33 ppm formaldehyde could be detected. High temperature absorption cross sections of CH 2 O and other selected species have been determined.