Shock Tube Studies Using a Novel Multipass Absorption Cell: Rate Constant Results For OH + H2and OH + C2H6

The reflected shock tube technique with a novel multipass absorption spectrometric detection method has been used to study two OH-radical reactions: OH + H 2 → H 2 O + H (1), and OH + C 2 H 6 → H 2 O + C 2 H 5 (2). Reaction 1 was chosen in order to test the method against earlier rate constant determinations. The measurements on both reactions were performed in single-shot experiments with low initial concentrations of hydroxyl radicals, [OH] 0 = (5−15) × 10 12 molecule cm -3, which allowed reliable isolation of the elementary reactions. The measured rate constants are: k 1 = 5.44 × 10 -11 exp(−3220 K/T) (832−1359 K), and k 2 = 1.10 × 10 -10 exp(−2537 K/T) (822−1367 K), both in cm 3 molecule -1 s -1 . The present study extends the experimental T-range for reaction 2. This new work and earlier lower-T studies have been combined to give a new evaluation, k 2 = 2.68 × 10 -18 (T/K) 2.224 exp(−373 K/T) cm 3 molecule -1 s -1 . An ab initio potential energy surface was additionally used to derive a theoretical expression for this reaction.