| Abstract
| - The mechanism of the H + HONO reaction (for which noexperimental data are available) has been elucidatedby ab initio molecular orbital calculations using modified G2 andBAC-MP4 methods. These results indicatethat the reaction occurs predominantly by two indirect metatheticalprocesses. One produces OH + HNOand H2O + NO from the decomposition of vibrationallyexcited hydroxyl nitroxide, HN(O)OH, formed byH atom addition to the N atom of HONO. The other producesH2O + NO from the decomposition ofvibrationally excited dihydroxylamino radical, N(OH)2,formed by H atom addition to the terminal O atom.These indirect displacement processes are much more efficient thanthe commonly assumed, direct H-abstractionreaction producing H2 + NO2. Atransition-state theory calculation for the direct abstraction reactionandRRKM calculations for the two indirect displacement processes give riseto the following rate constants, inunits of cm3 molecule-1s-1 for the 300−3500 K temperature rangeunder atmospheric conditions: kH2 =3.33 × 10-16T1.55exp(−3328.5/T), kOH = 9.36× 10-14T0.86exp(−2500.8/T),kH2O =1.35 × 10-17T1.89exp(−1935.7/T), where the rate constant for H2Oproduction represents the sum from both indirectdisplacementreactions.
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