Initiation in H2/O2: Rate constants for H2+O2→H+HO2 at high temperature

✍ Scribed by J.V. Michael; J.W. Sutherland; L.B. Harding; A.F. Wagner

• Book ID: 104270701
• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 202 KB
• Volume: 28
• Category: Article
• ISSN: 1540-7489
• DOI: 10.1016/s0082-0784(00)80543-3

✦ Synopsis

The reaction between H 2 and O 2 has been studied in a reflected shock tube apparatus between temperatures of 1662-2097 K and pressures of 400-570 torr with Kr as the diluent gas. O atom atomic resonance absorption spectrometry (ARAS) was used to observe absolute [O] t under conditions of low [H 2 ] 0 so that most secondary reactions were negligible. Hence, the observed [O] t was the direct result of the rate controlling reaction between H 2 and O 2 . Three different reactions were considered, but experimental and ab initio theoretical results both indicated that the process, H 2 ‫ם‬ O 2 → H ‫ם‬ HO 2 , is the most probable reaction. After rapid HO 2 dissociation, O atoms are then instantaneously produced by H ‫ם‬ O 2 → O ‫ם‬ OH. Using the ab initio result, conventional transition state theoretical calculations (CTST) with tunneling corrections give the expression T 2.4328 exp(‫629,62מ‬ K/T) cm 3 mol-th ‫81מ‬ k ‫ס‬ 1.228 ‫ן‬ 10 1 ecule ‫1מ‬ s ‫1מ‬ , applicable between 400 and 2300 K. This theoretical result agrees with the present experimental determinations and those at lower temperature, derived from earlier work on the reverse reaction. H ‫ם‬ O r OH ‫ם‬ OH (2) 2 2 H ‫ם‬ O r O ‫ם‬ H O (3) 2 2 2 H ‫ם‬ M r H ‫ם‬ H ‫ם‬ M (4) 2 and O ‫ם‬ M r O ‫ם‬ O ‫ם‬ M (5) 2 Reactions 1 and 2 have been the preferred initiation processes since reaction 3 requires multiple bond rearrangement and both diatomic dissociation reactions; 4 and 5 require substantially higher energy [2]. Reaction 2 was almost always the choice in shock tube induction delay experiments [3-6] until about 1985, with the value from Ripley and Gardiner [3], k 2 ‫ס‬ 4.16 ‫ן‬ 10 ‫21מ‬ exp(‫506,91מ‬ K/T) cm 3 molecule ‫1מ‬ s ‫1מ‬ , being typical. However, later flow tube studies at room temperature [7,8] on the reverse of