Formation of M(+) ions and electronic excitation under fast-atom bombardment conditions by using a liquid matrix.

Japan The mechanism for the formation of molecular ions M(+·) under fast-atom bombardment (FAB) conditions with a liquid matrix is discussed on the basis of the mass spectra of pyrene, coronene, and fullerene C60 obtained by using electron impact, gas-phase fast-atom bombardment, and gas-phase fast-molecule bombardment techniques. The obtained results suggest that formation of the M(+·) ions under FAB conditions is not due to direct collisions between analytes M and fast atoms A, but is due to collision interactions between M and recoiling matrix molecules B or matrix ions. It has been confirmed, furthermore, that the FAB conditions with a liquid matrix are sufficient in energy for formation of singly charged ions M(+·) and insufficient for the formation of multiply charged ions M (z+) (z=2, 3) of pyrene, coronene, and C60.