An Investigation of the D/H Addition−Elimination and H Atom Abstraction Channels in the Reaction D + H₂CO in the Temperature Range 296 K ≤T≤ 780 K

The reactions of H and D atoms with H2CO (H + H2CO → H2 + HCO (1.1), D + H2CO → HD + HCO (2.1), and D + H2CO → H + HDCO (2.2)) have been studied in the temperature range 296 K ≤ T ≤ 780 K in an isothermal discharge flow reactor with EPR detection of D and H atoms and LIF detection of HCO. Simultaneous measurements of the absolute concentration−time profiles of the three species established the occurrence of the D/H isotope exchange reaction (2.2) in addition to the H atom abstraction channel (2.1). The rate constants for the three reactions could be represented by the Arrhenius expressions k1.1(T) = (8.7 ± 1.9) × 1012 exp[−(14.5 ± 0.7) kJ mol-1/RT] cm3 mol-1 s-1, k2.1(T) = (1.2 ± 0.5) × 1013 exp[−(15.8 ± 0.8) kJ mol-1/RT] cm3 mol-1 s-1, and k2.2(T) = (5.9 ± 1.5) × 1012 exp[−(14.7 ± 1.0) kJ mol-1/RT] cm3 mol-1 s-1. A mechanistic analysis of reaction 2.2 using the unimolecular rate theory gave these estimates for the classical potential energy barrier heights in the addition of D and H atoms to H2CO: ΔE0(D + H2CO) = 1360 ± 100 cm-1 and ΔE0(H + H2CO) = 1540 ± 150 cm-1.