Ion-molecule and ion-surface collisions in hybrid and multiquadrupole mass spectrometers

Sohrab Habibi-Goudarzi, Purdue University

Abstract

Ion/molecule and ion/surface collisions are two major methods by which gas phase ions are characterized in tandem mass spectrometry. This work deals with developing novel instrumentation and applications in these areas. The stability of polyatomic ions upon collision with a surface was studied in a hybrid BQ (B = magnet, Q = quadrupole) mass spectrometer. Even-electron ions were generally found to reflect more readily than those with odd number of electrons. Reflection of an ion was also influenced by its degree of unsaturation and origin. A hybrid BQQ mass spectrometer was built to study dissociative charge exchange (DCE) of various ions with polyatomic neutrals. Products were collected at 90$\sp\circ$ with respect to the primary ion beam and the internal energy deposited in the target was shown to depend principally on the recombination energy of the reactant ion and the ionization energy of the target. The extent of fragmentation in the DCE spectra, in several cases, demonstrated strong dependance on the kinetic energy of the projectile ions. Three C$\sb6$H$\sb6$ isomers, benzene, 1,5-hexadiyne and 2,4-hexadiyne, were distinguished via the DCE method. Collisions between ions generated from dihalomethanes CH$\sb2$X$\sb2$ (where X = I, Br, or Cl) and a variety of targets were studied. Gaseous hydrocarbon targets were examined in a triple quadrupole mass spectrometer and solid targets in an orthogonal QQ mass spectrometer. Competition between charge exchange (CE), DCE, collision-induced dissociation (CID), surface-induced dissociation (SID) and sputtering of the surface adsorbates was examined. CE and DCE were favored at lower collision energies, and CID at either higher collision energies or when the CE reaction was endothermic or only slightly exothermic. In general, collisions of odd-electron incident ions with the surface favored hydrogen atom abstraction, neutralization and fragmentation, as opposed to reflection favored by even-electron projectiles. Sputtering of the surface adsorbates showed little dependence on the kinetic energy of the projectile ions. CE of C$\sb3$F$\sb6$ by a variety of atomic and molecular ions were used to characterize the energetics associated with formation of C$\sb3$F$\sb6\sp{+.}$. The internal energy of the nascent C$\sb3$F$\sb6\sp{+.}$ ion, assessed by observing the degree to which it fragmented, increased with the recombination energy of the CE reagent.

Degree

Ph.D.

Advisors

Cooks, Purdue University.

Subject Area

Analytical chemistry

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