Measurement of collision-induced dissociation rates for tantalum oxide ions in a quadrupole ion trap

A study of factors influencing the collision-induced dissociation (CID) rat e of strongly bound diatomic ions effected via resonance excitation in a qu adrupole ion trap is presented. From these studies, an approach to measurin g the CID rates is described wherein product ion recovery is optimized and the effect of competitive processes (e.g., parent ion ejection and product ion reactions) on rate measurements are prevented from influencing rate mea surements. Tantalum oxide ions (dissociation energy = 8.2 eV), used as a mo del system, were formed via reactions of glow discharge generated Ta+ ions with residual gases in the ion trap. Neon (0.5 mtorr) was found to be a mor e favorable target gas for the dissociation of TaO+ than He and Ar, but col lisional activation of TaO+ ions in neon during ion isolation by mass selec tive instability necessitated ion cooling prior to dissociation. A 25 ms de lay time at q(z) = 0.2 allowed for kinetic cooling of stored TaO+ ions and enabled precise dissociation rate measurements to be made. CID of TaO+ was determined to be most efficient at q(z) = 0.67 to (226 kHz for m/z 197). Su itable resonance excitation voltages and times ranged from 0.56 to 1.2 Vp-p and 1 to 68 ms, respectively. Under these conditions, measurement of rates approaching 80 s(-1) for the dissociation of TaO+ could be made without si gnificant complications associated with competing processes, such as ion ej ection. (J Am Soc Mass Spectrom 2000, 11, 1072-1078) (C) 2000 American Soci ety for Mass Spectrometry.