A Shock Tube Study of the Product Branching Ratio for the Reaction NH2 + NO Using Frequency-Modulation Detection of NH2

The product branching ratio of [NH 2 + NO → N 2 H + OH]:[NH 2 + NO → N 2 + H 2 O] has been determined in the temperature range of 1340−1670 K in a shock tube study with laser photolytic generation of the NH 2 radicals. Sensitive frequency-modulation detection of the NH 2 radical enables experiments with very low initial radical concentrations and, hence, virtually no interference from secondary reactions or dependence on the overall rate coefficient of the reaction. The branching ratio, α, defined as α = k 1a /( k 1a + k 1b ), increases from 0.42 at 1340 K to 0.53 at 1670 K. Over this temperature range our results can be expressed as α = 0.5 + (3.36 × 10 -4 )( T /K − 1600). A detailed error analysis yields an uncertainty in the values of α of ±0.02 near 1500 K, increasing to ±0.05 at the temperature extremes.