Thermal decomposition of formic acid at high temperatures in shock waves

Thermal decomposition of HCOOH has been studied from 1280 to 2030 K over a broad range of initial concentrations (0.07 to 1.6% in Ar) in a shock tube using a stabilized cw CO laser to monitor CO formation. The observed CO concentration profiles over the whole range of temperature and pressureemployed could be satisfactorily accounted for by the following two-channel molecular decomposition mechanism: (HCOOH + M over(→, 1) CO + H₂ O + M; HCOOH + M over(→, 2) CO₂ + H₂ O + M)89-1 with the following apparent second order rate constants in the pressure range 0.75-2.8 atm. (k₁ = 2.3 x 10¹⁵ exp (- 50, 000 ± 1700 / RT) c c mole^{- 1} sec^{- 1}; k₂ = 1.5 x 10¹⁶ exp (- 57, 000 ± 2800 / RT) c c mole^{- 1} sec^{- 1}) The values of these two rate constants were evaluated by the non-linear least squares fitting of the observed CO concentration profiles. The possibility of an alternative decomposition route involving the initial production of H atoms, instead of H₂, has also been considered. However, the rate constant evaluated from the kintic modeling of the CO formed at high temperatures cannot satisfactorily account for that observed at lower temperatures.