COLLISIONAL ACTIVATION OF PYRENE AND ANTHRACENE IN AN ION-TRAP MASS-SPECTROMETER

A quadrupole ion-trap mass spectrometer (ITMS) has been used to examine internal energy deposition and fragmentation pathways of ionized pyrene and anthracene. Through multiple collisional activation steps, large amounts of energy (tens of electronvolts) can be deposited and multiple-stage (MS(n)) dissociation reactions such as C16H10.+ --> C16H9+ --> C16H8.+ --> C14H6.+ --> C12H4.+ --> C8H2.+ --> C3H2.+ are observed. This particular reaction sequence requires approximately 29 eV, as estimated from the energy requirements for the individual dissociation reactions. While each individual reaction has an activation energy < 8 eV, the occurrence of the reaction sequence demonstrates the large total amount of energy which can be delivered in these experiments. The intriguing chemistry made accessible by multiple-stage activation (up to MS10) is exemplified by the formation of all-carbon fragment ions such as CK-7(.+) from the polycyclic aromatic hydrocarbon molecular ions. Under extreme activation conditions (high amplitude of the excitation pulse and longer activation time), the fragment ions observed in a single-stage (MS/MS) experiment include those having estimated activation energies as high as 17 eV. High-energy pathways can also be directly accessed in single-stage MS/MS experiments under less extreme activation conditions by introducing a small amount of xenon as the target gas with the helium buffer. This method has the additional advantage of high dissociation efficiency.