Negative ion-gas reaction studies using ion guides and accelerator mass spectrometry II: S−, SO− and Cl− with NO2 and N2O

Currently analysis of 36Cl by accelerator mass spectrometry (AMS) requires large facilities for separation of the isobar 36S. Previously, it has been shown possible to suppress S− by >6 orders of magnitude at low energies in a prototype radio-frequency quadrupole (RFQ) instrument by ion reactions in NO2 gas in the injection line of an AMS system. Reaction products for the negative ions S−, SO− and Cl− with NO2, and S− with N2O, have been surveyed in order to understand isobar attenuation plateaus and the losses of analyte ions. Ion energies were at eV levels, but had a large initial energy spread of at least several eV. Under these conditions, the aggregate total S− and SO− cross sections in NO2 were estimated to be 6.6 × 10−15 cm2 and 7.1 × 10−15 cm2 respectively and the major reaction channel observed was electron transfer producing NO2−. Other reaction products observed for S− were SO−, SO2−, NS−, and NSO2−. On the other hand, S−, SO− and NS− were found to be largely unreactive with N2O despite the existence of some highly exothermic reaction channels. When Cl− was injected into NO2, reaction products such as ClO− and NO2− were observed only at low levels suggesting that larger Cl− transmissions should be possible with some RFQ design modifications. The ClO− reaction product had only a small attenuation under the experimental conditions, despite having near resonant electron affinity with NO2.