Rong Feng

An improved tandem double-focusing mass spectrometer for neutralization—reionization and collisional activation studies

Abstract A four-sector EBEB mass spectrometer is modified to conduct neutralization—reionization mass spectrometry (NRMS), MS/MS/MS, and MS/NRMS/CAD-MS experiments. Four separate collision chambers enable the instrument to perform, for example, neutralization, neutral dissociation, reionization, and collisionally activated dissociation (CAD). The independent differential pumping systems of the key collision chambers and the improved general pumping system reduce the background pressure by more than one order of magnitude, with > 95% of collisions occurring within the collision system. This increases the collision efficiency by ∼ 70% and minimizes the cross-contamination of collision gases between regions, and for neutral lifetime measurements insures that neutral dissociation or reionization by gas admitted to the second collision chamber occurs there. Redesign of the Hg neutralization chamber to include low-temperature Hg condensation provides further differential pumping and increases the reproducibility of neutralization at high Hg pressure. A field ionization chamber provides a capability for detecting neutrals in high Rydberg states.