Studies of reactions of importance in the stratosphere. II. Reactions involving chlorine nitrate and chlorine dioxide

Abstract

The rate of formation of chlorine nitrate, ClO+NO2+M→ClONO2+M, has been studied over the temperature range 250–356 °K and the pressure range 1–5 torr using the discharge flow technique with mass spectrometry for detection. The resulting low pressure third order reaction rate constant in N2 is given by the Arrhenius expression k N2=4.40±0.66 ×10−33 exp(1087±70/T)cm6 molecule−2 sec−1. Helium was found to be one‐half as effective as N2 as a third body for this reaction. No reaction of ClONO2 with NO, NO2, O3, or HCl could be observed. Upper limits of 4.×10−17, 2.×10−17, 7.×10−17, and 1.2×10−15 cm3 molecule−1 sec−1 for the respective bimolecular reaction rate constants preclude the importance of these reactions as sinks for ClONO2 in the stratosphere. A heterogeneous reaction, ClONO2+HClsurface→HONO2+Cl2, was observed, and may be useful as a selective reaction for the measurement of chlorine nitrate in the stratosphere. An upper limit of 10−16 cm3 molecule−1 sec−1 was found for the reaction ClO+O3→OClO+O2 and an upper limit of 5.×10−14 cm3 molecule−1 sec−1 for the reaction ClO+O3→ClOO+O2 at 298 °K. The rate constant for the reaction OClO+O3→ClO3 +O2 was found to be 1.20±0.15×10−19 cm3 molecule−1 sec−1 at 298 °K by a static method, the concentrations of OClO and O3 being followed by optical absorption. These results, combined with the calculated photolysis constant for OClO of 7.6×10−2 sec−1, rule out of the successive oxidation of chlorine as a path to the photochemically stable species perchloric acid.