PLASMA DESORPTION MASS-SPECTROMETRY OF SMALL STRAIGHT-CHAIN AND CYCLIC ALKENES

The plasma desorption mass spectra of straight-chain and cyclic alkene s and cyclic alkadienes were examined to gain a better understanding o f the influence of structure on mass spectral characteristics. The res ults are compared with electron impact data because the excitation and ionization mechanisms are influenced by electronic transitions, and a re also compared with chemical ionization data because of the possibil ity that ion-molecule reactions may occur during the desorption proces s. Several ions related to the molecular ion by gain or loss of hydrog en are produced in all spectra. For plasma desorption, our data sugges t that energy dissipation in the solid phase influences the intensity of these ions. A chemical ionization-like process is proposed to expla in the gain or loss of hydrogen atoms. The spectra of conjugated and u nconjugated cyclooctadienes give evidence of the formation of benzene- like ions. The fragment ions produced from these compounds indicate an electron impact-like fragmentation mechanism, while fragments from ot her compounds suggest a chemical ionization-like fragmentation process .