Multiple excitation collisional activation (MECA) and reactivities of selected niobium-carbon cluster ions in the gas phase
Abstract
Several applications of a new method for FTICR mass spectrometry, dubbed multiple excitation collisional activation (MECA) are described. These include synthesizing pure and bimetallic cluster ions and increasing energy deposition in hard-to-fragment cluster ions such as buckyball derivatives. The chemistry of selected niobium-carbon cluster ions with various reagents, together with theoretical studies, is investigated using an FTICR mass spectrometer coupled to a supersonic expansion source to probe their structures. For Nb$\sb6$C$\sb7\sp+$, sequential attachment reactions occur leading to the predominant product Nb$\sb6$C$\sb7$L$\sb4\sp+$. Ab initio calculations of Nb$\sb6$C$\sb7$, performed by Professor Sabre Kais and co-workers, and experimental results suggest a structure consisting of two cubes with one carbon at the exact inversion center of the D$\rm\sb{2h}$ symmetry. Nb$\sb4$C$\sb4$ and Nb$\sb5$C$\sb6$ are also treated theoretically. Nb$\sb8$C$\sb{12}\sp+$ reacts both with polar (water, methanol and 2-butanol) and $\pi$-bonding molecules (acetonitrile and benzene-$d\sb6$) via sequential association reactions and truncates at 4 attachments. These "titration" experimental results provide supporting evidence that the geometric structure of Nb$\sb6$C$\sb{12}\sp+$ is the theoretically predicted more stable T$\rm\sb{d}$ symmetry and not the originally proposed T$\rm\sb{h}$ structure. Oxidation of Nb$\sb8$C$\sb{12}\sp+$ occurs when it reacts with halogen containing molecules such as CH$\sb3$I and CH$\sb3$Br through valence electron donation from Nb$\sb8$C$\sb{12}\sp+$ to the halogen atoms. Pseudo-first-order kinetics indicate that the Nb$\sb8$C$\sb{12}\sp+$ species formed in the supersonic source and thermalized in the FTICR cell, consists of single isomeric structure.
Degree
Ph.D.
Advisors
Freiser, Purdue University.
Subject Area
Analytical chemistry|Organic chemistry
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