Correlated phase space distributions of ions in an orthogonal time-of-flight mass spectrometer

Abstract

A prototype orthogonal time-of-flight (oTOF) mass spectrometer equipped with a thermal ionization (TI) source and an electron impact (EI) source was designed and constructed. Low energy ion beams (∼10 eV) were generated and ejected by a two-stage acceleration configuration into the TOF mass analyzer operating in the linear mode. Interfaces between the sources and the analyzer were optimized so as to reduce the contribution of the turn-around time on the final resolving power of the instrument. The concept of space-velocity correlated ion beams is described in this context. Experiments with variable detector positions were performed and spectral line widths of ∼2 ns were achieved at the end of a 45 cm long linear oTOF MS with ∼3.7 keV energy ions. A new theoretical approach is developed for linear phase space distributions of ions at the start of the TOF experiment. Analytical solutions for first and second-order focusing instruments are presented.