REACTIONS OF SIF5- WITH ATMOSPHERIC TRACE GASES - ION CHEMISTRY FOR CHEMICAL-IONIZATION DETECTION OF HNO3 IN THE TROPOSPHERE

The reactions of SiF5- with a series of trace atmospheric species were studied using the flowing afterglow technique at 293 K. SiF5- reacts at the collision rate by fluoride transfer with HI and SO3. SiF5- reac ts rapidly with HNO3 to primarily form a strongly bound cluster ion. S iF5- also forms more weakly bound cluster ions with HCO2H, HCl, CH3CO2 H, and H2O. SiF5- was found to be unreactive with HBr, N2O5, HO2NO2, N O2, ClONO2, O-3, SO2, CH3NO3, CH3C(O)O2NO2, CO2, H2O, and NH3. These r esults demonstrate that SiF5- is an excellent reagent ion for the sele ctive detection of HNO3 in ambient air with a chemical ionization mass spectrometer.