Electron capture chemistry of CBrCl 3 at atmospheric pressure by mass spectrometry and the photodetachment-modulated electron capture detector

Abstract

Measurements are reported of the electron capture (EC) chemistry of CBrCl 3 in a buffer gas at atmospheric pressure over the temperature range 30–250°C. These measurements are made with an atmospheric pressure ionization mass spectrometer (APIMS) and with a recently developed atmospheric pressure transducer called the photodetachment-modulated EC detector (PDM-ECD). It is shown that the initial reaction of CBrCl 3 with thermal electrons proceeds by dissociative EC to form primarily Br − and some Cl −. At low temperatures the neutral products formed in the initial reaction, CCl 3 and CBrCl 2, are also shown to undergo rapid EC to form additional amounts of Cl −. At high temperatures, however, there is no evidence for EC by CCl 3 and CBrCl 2, because of what is thought to be a faster wall reaction which effectively destroys these radical species. It is concluded that the stoichiometry of the reaction of electrons with CBrCl 3 and with CCl 4 in an EC detector (ECD) will be between 1.0 and 2.0 and will be strongly dependent on temperature. These results are compared with previous studies of the EC chemistry of CBrCl 3 by APIMS and by the flowing afterglow/Langmuir probe (FALP) technique.