LAUSR

Abstract In this study we present an investigation of the negative ion-molecule chemistry of pentachloroethane (PCE) in air based ion mobility spectrometry and ion mobility spectrometry–mass spectrometry systems. The observed product ions are Cl − , produced by dissociative electron attachment, and Cl − ·HOO resulting from a reaction with O 2 − . Based upon the moisture content of the system, these ions can be observed as a doublet in a ‘dry’ system or as a singlet in a ‘wet’ system. The nature of the Cl − ·HOO product ion was investigated by using isoflurane (ISOF) as a probe to monitor the changing ratios of Cl − and Cl − ·HOO as the PCE concentration decreased. This confirmed the origins of the two product anions. Electronic structure calculations are provided. These have aided the understanding of the reaction processes observed.