What are the reasons for the kinetic stability of a mixture of H-2 and O-2?

Citation
M. Filatov et al., What are the reasons for the kinetic stability of a mixture of H-2 and O-2?, J PHYS CH A, 104(51), 2000, pp. 12014-12020
Citations number
42
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF PHYSICAL CHEMISTRY A
ISSN journal
10895639 → ACNP
Volume
104
Issue
51
Year of publication
2000
Pages
12014 - 12020
Database
ISI
SICI code
1089-5639(200012)104:51<12014:WATRFT>2.0.ZU;2-U
Abstract
Calculations at the (14,10)CASSCF/6-31G** and the MR-(S)DCI/cc-pVTZ levels are employed to answer the title question by studying three possible modes of reaction between dioxygen and dihydrogen molecules at the ground triplet state and excited singlet state of O-2. These reaction modes, which are an alogous to well-established mechanisms for oxidants such as transition meta l oxene cations and mono-oxygenase enzymes, are the following: (i) the conc erted addition, (ii) the oxene-insertion, and (iii) the hydrogen abstractio n followed by hydrogen rebound. The "rebound" mechanism is found to be the most preferable of the three mechanisms. However, the barrier of the H-abst raction step is substantial both for the triplet and the singlet states of O-2, and the process is highly endothermic (>30 kcal/mol) and is unlikely t o proceed at ambient conditions. The calculations revealed also that the lo west singlet state of O-2 has very high barriers for reaction and therefore cannot mediate a facile oxidation of H-2 in contrast to transition metal o xenide cation catalysts and monooxygenase enzymes. This fundamental differe nce is explained.