Kinetics of hydroxyl radical reactions with formaldehyde and 1,3,5‐trioxane between 290 and 600 K

Absolute rate constants are measured for the reactions: OH + CH₂O, over the temperature range 296–576 K and for OH + 1,3,5‐trioxane over the range 292–597 K. The technique employed is laser photolysis of H₂O₂ or HNO₃ to produce OH, and laser‐induced fluorescence to directly monitor the relative OH concentration. The results fit the following Arrhenius equations: k (CH₂O) = (1.66 ± 0.20) × 10⁻¹¹ exp[−(170 ± 80)/RT] cm³ s⁻¹ and k(1,3,5‐trioxane) = (1.36 ± 0.20) × 10⁻¹¹ exp[−(460 ± 100)/RT] cm³ s⁻¹. The transition‐state theory is employed to model the OH + CH₂O reaction and extrapolate into the combustion regime. The calculated result covering 300 to 2500 K can be represented by the equation: k(CH₂O) = 1.2 × 10⁻¹⁸ T^2.46 exp(970/RT) cm³ s⁻¹. An estimate of 91 ± 2 kcal/mol is obtained for the first CH bond in 1,3,5‐trioxane by using a correlation of CH bond strength with measured activation energies.