OBSERVATION OF AN H/D-ISOTOPE EXCHANGE CHANNEL IN THE REACTION D+H2CO

The reactions of H and D atoms with H2CO, H+H2CO --> H-2 + HCO, (1) D+H2CO --> HD + HCO, (2a) --> H + HDCO, (2b) were studied in an isothermal discharge flow reactor at room temperature with EPR detection of H and D atoms and LIF detection of HCO radicals. Simultaneous measurements of the absolute concentration-versus-time profiles of D, H, and HCO in the D + H2CO system established the occurrence of the H/D isotope exchange reaction (2b), which competes with the usually assumed direct H atom abstraction channel (2a). The room temperature rate constants of the two reaction channels were found to be k2a (296 K) = (1.9 +/- 0.5) x 10(10) cm3/mol s, k2b (296 K) = (1.5 -/+ 0.4) x 10(10) cm3/mol s.