Absolute absorption cross-section measurements on NO3. Evaluation of the titration of NO3 by NO in the determination of absolute concentrations

Abstract

The absorption cross-section of NO₃ at λ= 662 nm and at room temperature was found to be (2.23 ± 0.35)× 10^–17 cm² molecule^–1. Error limits are 95% confidence limits for random errors. A discharge flow apparatus was used to prepare NO₃ by the reaction of F atoms with HNO₃. The absolute concentration of NO₃ in the absorption cell was determined by titration with NO. A stoicheiometric factor for the removal of NO₃ was calculated using numerical integration of the kinetic equations derived from a simple reaction scheme. This factor is not always unity, and we indicate the consequences of erroneously assuming 1 : 1 stoicheiometry for NO₃ removal by NO. The influence on the calculated value of σ of the initial concentrations of F atoms and HNO₃ is discussed. The role of possible interfering reactions is also considered.