PLASMA DESORPTION MASS-SPECTROMETRY OF SMALL STRAIGHT-CHAIN AND CYCLIC ALKENES
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The plasma desorption mass spectra of straightchain and cyclic alkenes and cyclic alkadienes were examined to gain a better understanding of the influence of structure on mass spectral characteristics. The results are compared with electron impact data because the excitation and ionization mechanisms are influenced by electronic transitions, and are also compared with chemical ionization data because of the possibility that ionmolecule reactions may occur during the desorption process. Several ions related to the molecular ion by gain or loss of hydrogen are produced in all spectra. For plasma desorption, our data suggest that energy dissipation in the solid phase influences the intensity of these ions. A chemical ionizationlike process is proposed to explain the gain or loss of hydrogen atoms. The spectra of conjugated and unconjugated cyclooctadienes give evidence of the formation of benzenelike ions. The fragment ions produced from these compounds indicate an electron impactlike fragmentation mechanism, while fragments from other compounds suggest a chemical ionizationlike fragmentation process. Copyright 1995 John Wiley & Sons, Ltd.
