Gas phase reactions of negative ions with ClONO2

The reactions of the halide anions (F-, Cl-, Br-, and I-), NO2-, SF6-, CO3- and CO4- with ClONO2 have been studied at room temperature in a flowing af terglow apparatus. All these reactions are found to proceed at the collisio n limit and the experimental data are compared with literature values. The reaction of I- with ClONO2 was studied at stratospheric pressures and tempe ratures in view of its use as a possible precursor ion for the measurement of stratospheric N2O5+ClONO2 mixing ratio height profiles by chemical ioniz ation mass spectrometry. No pressure or temperature dependence of the rate constant has been observed. In order to correct the observed rate constants for HNO3 impurities, the reaction rate constants of F-, Br-, and NO2- with HNO3 have also been determined. In addition, the apparent second-order clu stering rate constant of NO3- with ClONO2 in Ar/N-2 and Ar/He mixtures has been measured. (C) 2001 Elsevier Science B.V.