Contrasting behavior of tetracene and perylene in collision-induced dissociation: a theoretical interpretation.

Dimethyl ether chemical ionization mass spectrometry of polycyclic aromatic hydrocarbons (PAHs) leads to [M + 13](+) and [M + 45](+) ions. The process leading to these ions is sensitive to the proton affinity of the PAH. Collision-induced dissociation observations on [M + 45](+) ion also show that tetracene has a peculiar reactivity in comparison with perylene, despite the similar physico-chemical properties of these two molecules. Ab initio calculations were used to establish a potential energy profile for the mechanistic pathway of [M + 13](+) and [M + 45](+) formation. [M + 45](+) ions result from the addition of CH(3)-O-CH(2)(+) to PAHs. A 1,2-hydride transfer followed by a 1,4-proton transfer and a loss of methanol subsequently lead to the formation of [M + 13](+) ions. For tetracene, the 1,2-hydride transfer does not occur, as it would lead to a thermodynamically unstable non-planar ion. Copyright 1999 John Wiley & Sons, Ltd.