EXAMINATION OF SPUTTERED ION MECHANISMS LEADING TO THE FORMATION OF C7H7-INDUCED DISSOCIATION (SID) TANDEM MASS-SPECTROMETRY (MS( DURING SURFACE)MS) OF BENZENE MOLECULAR CATIONS/

Recent work reported in the literature has shown new evidence of a spu ttered ion mechanism for associative ion surface reactions occurring d uring surface induced dissociation (SID) tandem mass spectrometry (MS/ MS). In the context of a sputtered ion mechanism, we have studied sele cted routes to the formation of C7H7+ during the low-energy collision (ca. 30 eV) of benzene molecular ions with surfaces covered with a hyd rocarbon overlayer. A key approach utilized in this work is the use of gas phase ion molecule chemistry to model reactive ion surface collis ions. Benzene, H-2(6)-labeled benzene, and C-13(6)-labeled benzene hav e been examined by SID and collision activated dissociation (CAD). The CAD experiments have been used to investigate the fragmentation of hy drocarbon adducts of benzene and labeled benzene formed by methane and isobutane chemical ionization (CI) as models of those ions which may be formed via a sputtered ion mechanism during SID. In addition, the t hermodynamics of many of the possible sputtered ion routes to the form ation of C7H7+ have been compared using experimental heats of formatio n as well as total energies and zero-point vibrational energies (ZPVE) obtained by ab initio (MP2 6-31G//HF 6-31G*) calculations. While the re are several seemingly viable sputtered ion routes to the formation of C7H7+ during SID of benzene molecular ions, the combination of ther modynamic considerations and experimental results suggest that a likel y sputtered ion route involves the reaction of neutralized benzene ion s with C3H5+ ions (sputtered from the hydrocarbon overlayer) followed by the loss of ethene.