I. Fundamental studies in molecular secondary ion mass-spectrometry and related mass-spectral techniques. II. Surface modification by soft landing of reagent ion beams

Lisa Diane Detter, Purdue University

Abstract

A detailed secondary ion mass spectrometry (SIMS) study of Ag(I) and Cu(I) isocyanide complexes of the type (M(CNR)$\sb4$) X (X = ClO$\sb4$ or PF$\sb6$) is presented. Cross- and isotopic-labeling experiments have provided insight into fragmentation mechanisms. Ligand exchange occurred when mixtures were examined. This provides evidence for extensive molecular-mixing in SIMS even under low energy conditions. Mass analysis of the 18-electron 1,4-diaza-1,3-butadiene complexes (Cr(CO)$\sb3$(CNR)(R$\sp\prime$-DAB)) was undertaken using SIMS, EI, positive- and negative-ion chemical ionization mass spectrometry. With the exception of PICI spectra, abundant molecular ions were not present. In all instances, well-defined structurally informative fragments were identified that resulted from loss of CO and/or intact RNC and R$\sp\prime$-DAB ligands. Cleavage of RNC (dealkylation) occurred in SIMS and EI to give (Cr(CNH)) $\sp+$, whereas only in NICI were fragments observed in which the cyano moiety (Cr(CN)) $\sp-$ was present. Highly abundant carbonyl-containing fragments were seen only in the case of NICI spectra. A similar comparative mass spectral study of complexes of the type M(CO)$\sb2$(CNR)$\sb2$(PR$\sbsp{3}{\prime})\sb2$ (M = Mo or W) was carried out using FAB, EI, PICI and NICI methods. The FAB mass spectra provide the most useful structural information with the observation of molecular ions and, in some instances, the pseudomolecular ions (M + H)$\sp+$. Fragmentation ions arising from competitive ligand loss (CO vs. RNC vs. PR$\sbsp{3}{\prime}$) were observed, as well as those formed by loss of H from fragment ions and dealkylation of RNC. The NICI spectra showed an abundance of ions that resulted from ligand redistribution reactions. Further developments of the technique called Ion Beam Induced Synthesis (IBIS) are presented. Experimental parameters for improving SIMS spectral quality and reproducibility are discussed. Experiments which employed accelerated copper ions impacting onto organic pellets caused beam-induced mixing and thus enhanced cationization in the SIMS spectra. Coating substrates with silver films modified the surface structure so as to promote hydrogenation and subsequent hydrogenolysis reactions. Labeling experiments suggest that hydrogen arises from internal decomposition of the analyte, and the SIMS data suggest that a stepwise reduction process occurs.

Degree

Ph.D.

Advisors

Walton, Purdue University.

Subject Area

Chemistry

COinS