Analysis of metastable decay by time-of-flight coincidence and kinetics energy measurements

摘要

A procedure for fragmentation pattern analysis of metastable ions, emitted in photon or ion induced desorption processes, is described. The method is based on a combination of three well-established techniques, namely: time-of-flight (TOF), coincidence counting, and electrostatic energy analysis in reflectron mass spectrometers. The key improvement comes from a judicious selection of the electrostatic mirror voltages for running the coincidence measurements in the best signaloise conditions. The TOFs of stable species, as well as those of the neutral and ion fragments produced by all expected unimolecular-binary decays occurring in the field-free region before the mirror, are calculated and plotted as a function of the mirror voltage. The mirror voltage for coincidence measurements are selected after comparison of these dynamics plots of reflected and nonreflected species with experimental noncoincidence TOF spectra. To illustrate this procedure, the (LiF)_nLi~(+*) → (LiF)_(n-m)Li~+ + (LiF)_m~0 fragmentation pattern is analyzed.