[en] This paper describes a coincidence method for studying metastable ion decompositions with a ²⁵²Cf time of flight mass spectrometer. An electrostatic mirror is used to reflect ions which are detected by a set of annular channel plates while neutrals resulting from ''in flight'' decompositions are counted by channel plates placed behind the mirror. Two simultaneous time of flight (T.O.F.) measurements (ions and neutrals) are recorded event by event using the same start signals. Therefore correlated reflex spectra can be obtained by setting electronically time ''windows'' on the neutral T.O.F. These windows correspond to masses which have decayed in flight. The charged fragments are then selected in the reflex spectra by this method of coincidences. In flight decays can therefore be identified. Other ionization-desorption techniques can be used as well. A few simple examples are presented