Reaction Rate Constant of CH2O + H = HCO+ H2Revisited: A Combined Study of Direct Shock Tube Measurementand Transition State Theory Calculation.

The rate constant of the H-abstractionreaction of formaldehyde(CH2O) by hydrogen atoms (H), CH2O + H = H2+ HCO, has been studied behind reflected shock waves withuse of a sensitive mid-IR laser absorption diagnostic for CO, overtemperatures of 1304–2006 K and at pressures near 1 atm. C2H5I was used as an H atom precursor and 1,3,5-trioxaneas the CH2O precursor, to generate a well-controlled CH2O/H reacting system. By designing the experiments to maintainrelatively constant H atom concentrations, the current study significantlyboosted the measurement sensitivity of the target reaction and suppressedthe influence of interfering reactions. The measured CH2O + H rate constant can be expressed in modified Arrhenius from as kCH2O+H(1304–2006 K, 1 atm)= 1.97 × 1011(T/K)1.06exp(−3818 K/T) cm3mol–1s–1, with uncertainty limits estimated to be +18%/–26%.A transition-state-theory (TST) calculation, using the CCSD(T)-F12/VTZ-F12level of theory, is in good agreement with the shock tube measurementand extended the temperature range of the current study to 200–3000K, over which a modified Arrhenius fit of the rate constant can beexpressed as kCH2O+H(200–3000K) = 5.86 × 103(T/K)3.13exp(−762 K/T) cm3mol–1 s–1. [ABSTRACT FROM AUTHOR]