Pressure Effects on Mass Spectra of Picoline N-Oxides

Abstract

The mass spectral fragmentations of 2-, 3-and 4-picoline N-oxides were studied at various sample pressures. The relative intensities of the fragment ions greatly depend upon the sample pressure even at pressures in the normal working range. From the patterns of logarithmic ion intensity-pressure curves, the formation mechanisms of the fragment ions are classified into four types of reactions. They are the unimolecular decomposition of the molecular ion, the fragmen-tations including some intermediate ions, the formation of secondary ions, and the fragmentations including two or three kinds of these reactions. The fragmentations including the intermediate ions may occur in the first step of decompositions concerned with the skeletal rearrangements of the molecular ion.