Absolute rate of the reaction of N(4<i>S</i>) with NO from 196–400 K with DF–RF and FP–RF techniques

Abstract

Rate constants for the reaction of N(4S) with NO have been measured from 196–400 K with two independent techniques both which utilize resonance fluoresence detection for temporal analysis of N(4S). The reaction has been studied at 196, 297, and 370 K by the discharge flow-resonance fluorescence technique (DF-RF) and the measured rate constant is best represented by the temperature independent value of (2.7±0.4) ×10−11 cm3 molecule−1 s−1. The technique of flash photolysis-resonance fluorescence (FP-RF) has been used to study the reaction at 233, 298, and 400 K, and the results are best represented by the temperature independent value of (4.0±0.2) ×10−11 cm3 molecule−1 s−1. Combination of the results suggests a value of (3.4±0.9) ×10−11 cm3 molecule−1 s−1 between 196–400 K. In this work discrimination between O(3P) atom and N(4S) atom fluorescence was necessary, and this was accomplished by inclusion of an O atom resonance line filtering section as an integral part of the resonance lamp. The suggested value for the rate constant is combined with a statistical mechanical evaluation of the equilibrium constant for N(4S)+NO=N2+O(3P) to give a revised estimate for the rate constant of the back reaction. The back reaction is important in the Zeldovich mechanism for thermal production of NO in combustion systems. The rate constant is also theoretically discussed in terms of collision theory.