Reactions of SiF 5− with atmospheric trace gases: ion chemistry for chemical ionization detection of HNO 3 in the troposphere

Abstract

The reactions of SiF 5 − with a series of trace atmospheric species were studied using the flowing afterglow technique at 293 K. SiF 5 − reacts at the collision rate by fluoride transfer with HI and SO 3. SiF 5 − reacts rapidly with HNO 3 to primarily form a strongly bound cluster ion. SiF 5 − also forms more weakly bound cluster ions with HCO 2H, HCl, CH 3CO 2H, and H 2O. SiF 5 − was found to be unreactive with HBr, N 2O 5, HO 2NO 2, NO 2, ClONO 2, O 3, SO 2, CH 3NO 3, CH 3C(O)O 2NO 2, CO 2, H 2O, and NH 3. These results demonstrate that SiF 5 − is an excellent reagent ion for the selective detection of HNO 3 in ambient air with a chemical ionization mass spectrometer.