NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. A brief introduction (Chapter 1) gives a general overview of the results presented in this thesis, and is followed by five chapters which concern ion cyclotron resonance spectroscopy (ICR) studies of transition metal complexes, trifluorophosphine, and methylsilanes in the gas phase. An ancillary study on the photoionization mass spectrometry (PIMS) of the methylsilanes is also included. Chapter II discusses the gas phase ion chemistry of ([eta superscript 5] - C5H5)NiNO. The dissociative bond energies, D(B-CpNi[superscript +]) [...], are obtained by measuring equilibrium constants for reactions involving CpNi[superscript +] transfer between appropriate base pairs. A wide variety of reactions effected by CpNi[superscript +], including dehydrohalogenation, dehydration, dehydrogenation, decarbonylation, and alkylation processes are observed, and reaction mechanisms proposed. Chapter III presents a detailed study of the sequential alkylation of CpNi[superscript +] and CpFe[superscript +] by d3-methyl bromide. A reaction mechanism involving oxidative addition of the metal to the weak carbon-bromine [sigma]-bond is presented. The first observed example of a ligand displacement reaction involving an anionic transition metal complex, in which PF3 displaces CO from CpCo(CO)[superscript -], is reported in Chapter IV. This result leads directly to the conclusion that PF3 is a stronger [pi]-acceptor ligand than CO towards CpCo[superscript -] in the gas phase. Additionally, the negative ion chemistry of CpCo(CO)2 both alone and in mixtures with various ligands is presented. The gas phase basicity, or proton affinity, of phosphorus tri-fluoride is determined in Chapter V. The results are discussed in terms of contributions from inductive and hyperconjugative interactions involving p[subscript pi]-d[subscript pi] bonding in HPF3[superscript +]. Ion-molecule reactions of mixtures of PF3 with SiF4, BF3, SF6, NF3, CH3F, and (CH3)2CO are briefly considered; various thermochemical considerations are used to determine the energetics of formation of the PF2[superscript +], PF4[superscript +], and CH3PF3[superscript +] ions observed in these mixtures. Several examples of gas phase chain reaction which proceed through ionic intermediates are presented in Chapter VI. Chain propagation reactions involve hydride and fluoride transfer between pairs of siliconium ions R1[superscript +] and carbonium ions R2[superscript +], for which D(R1[superscript +]-F[superscript -]) [...] D(R2[superscript +]-F[superscript -]) and D(R1[superscript +]-H[superscript -])[...] D(R2[superscript +]-H[superscript -]). Photoionization efficiency for the low energy fragment ions (P-H)[superscript +], (P-H2)[superscript +], and (P-CH4)[superscript +] for the series of methylsilanes, (CH3)nH4-nSi (n = 0-3), are reported in Chapter VII. Appearance potentials for the (P-H)[superscript + siliconium ion fragments afford accurate calculation of the hydride affinities, D(R3Si[superscript +] -H[superscript -]) of these species.