Reaction Rate Constant of CH sub(2)O + H = HCO + H sub(2) Revisited: A Combined Study of Direct Shock Tube Measurement and Transition State Theory Calculation

The rate constant of the H-abstraction reaction of formaldehyde (CH sub(2)O) by hydrogen atoms (H), CH sub(2)O + H = H sub(2) + HCO, has been studied behind reflected shock waves with use of a sensitive mid-IR laser absorption diagnostic for CO, over temperatures of 1304-2006 K and at pressures near 1 atm. C sub(2)H sub(5)I was used as an H atom precursor and 1,3,5-trioxane as the CH sub(2)O precursor, to generate a well-controlled CH sub(2)O/H reacting system. By designing the experiments to maintain relatively constant H atom concentrations, the current study significantly boosted the measurement sensitivity of the target reaction and suppressed the influence of interfering reactions. The measured CH sub(2)O + H rate constant can be expressed in modified Arrhenius from as k sub(CH) sub(2)+H1304-2006 K, 1 atm) = 1.97 10 super(11)(T/K) super(1.06) exp(-3818 K/T) cm super(3) mol super(-1)s super(-1), with uncertainty limits estimated to be +18%/-26%. A transition-state-theory (TST) calculation, using the CCSD(T)-F12/VTZ-F12 level of theory, is in good agreement with the shock tube measurement and extended the temperature range of the current study to 200-3000 K, over which a modified Arrhenius fit of the rate constant can be expressed as k sub(CH) sub(2)+H200-3000 K) = 5.86 10 super(3)(T/K) super(3.13) exp(-762 K/T) cm super(3) mol super(-1 )s super(-1).