Metastable Ions and Isotope Effects in the Mass Spectra of Propane and Deuterated Propanes

Metastable transitions occurring in the mass spectrum of C3H8, CH3CD2CH3, CD3CH2CD3, and C3D8 have been investigated by means of the defocusing technique using a double-focusing mass spectrometer. In addition, detailed calculations of the decomposition of propane ions have been carried out, using the quasiequilibrium theory of mass spectra. Very strong isotope effects are observed and are accounted for quantitatively, and it is concluded that the quasiequilibrium theory provides an adequate framework for the description of both metastable ions and the general fragmentation processes responsible for the mass spectra of the deuterated propanes.