Determination of the nitrogen trioxide + nitrogen dioxide .fwdarw. nitric oxide + oxygen + nitrogen dioxide rate constant by infrared diode laser and Fourier transform spectroscopy

Abstract

The rate constant, k{sub 1}, at 296 K for the reaction NO{sub 3} + NO{sub 2} {yields} NO + NO{sub 2} + O{sub 2} has been determined relative to the rate constant, k{sub 2}, for the reaction NO{sub 3} + NO {yields} 2NO{sub 2} by direct measurement of (NO) and (NO{sub 2}) in a steady-state situation where the effect of the thermal decomposition of NO{sub 3} was negligible. NO{sub 3} was generated in the presence of a large excess of NO{sub 2}. The (NO{sub 2}) was determined by FTIR while the (NO) was measured with a tunable diode laser spectrometer operated in second-harmonic detection mode. From a series of 18 experiments performed at 50- and 15-Torr total pressures, the rate constant k{sub 1} was calculated at 296 K as k{sub 1} = ((1.5 {plus minus} 0.28) {times} 10{sup {minus}26})/k{sub 2} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}. Assuming the rate constant k{sub 2} = (3.0 {plus minus} 0.9) {times} 10{sup {minus}11} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1}, a k{sub 1} value at 296 K equal to (5.1 {plus minus} 1.8) {times} 10{sup {minus}16} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} is calculated.