Bonding and electronic structure of XeF3-.

The xenon-fluoride bond dissociation energy in XeF3- has been measured by using energy-resolved collision-induced dissociation studies of the ion. The measured value, 0.84 +/- 0.06 eV, is higher than that predicted by electrostatic and three-center, four-electron bonding models. The bonding in XeF3- is qualitatively described by using molecular orbital approaches, using either a diradical approach or orbital interaction models. Two low-energy singlet structures are identified for XeF3-, consisting of Y- and T-shaped geometries, and there is a higher energy D3h triplet state. Electronic structure calculations predict the Y geometry to be the lowest energy structure, which can rearrange by pseudorotation through the T geometry. Orbital correlation diagrams indicate that that ion dissociates by first rearranging to the T structure before losing fluoride.

In situ generation of HCN for mass spectrometric studies.

Hydrogen cyanide (HCN) for use in ion preparation can be generated in the gas phase by the neutral-neutral reaction of trimethylsilyl cyanide (Me(3)SiCN) and water in a flowing afterglow mass spectrometer. We demonstrate that the approach can be used to generate a wide range of HCN solvated ions such as F(-)(HCN), Cl(-)(HCN), CN(-)(HCN), PhNO(2)(.-)(HCN), Me(3)SiO(-)(HCN),and PhSiF(4)(-)(HCN), many of which are otherwise difficult to generate. The bond dissociation energy of CN(-)(HCN), generated by using this approach, has been measured by using energy-resolved collision-induced issociation (CID) to be 0.87 +/- 0.07 eV.

Fluorotrimethylsilane affinities of anionic nucleophiles: a study of fluoride-induced desilylation.

In this study, preparation and decomposition of five novel pentavalent fluorosiliconates, RSi(CH3)3F- (R = CH3CH2O, CF3CH2O, (CH3)2CHO, (CH3)3SiO, and (CH3)3SiNH) is used to investigate the process of fluoride-induced desilylation. The siliconates were characterized by collision-induced dissociation and energy-resolved mass spectrometry. Decomposition of RSi(CH3)3F- leads to loss of the nucleophile R- and FSi(CH3)3, except in the case of (CH3)3SiNHSi(CH3)3F-, where HF loss is also observed. Ion affinities for FSi(CH3)3 have been measured for all five nucleophiles, and compare well with computational predictions. The observed trend of the bond dissociation energies resembles the trend of deltaH(acid) values for the corresponding conjugate acids, RH. Additionally, this data has been incorporated with existing thermochemistry to derive fluoride affinities for four of the silanes (R = CH3CH2O, (CH3)2CHO, (CH3)3SiO, and (CH3)3SiNH). We use the fluoride affinity of the silanes and the FSi(CH3)3 affinity of the departing nucleophilic anion to assess the feasibility of fluoride-induced desilylation of the silanes examined in this work.

Bond dissociation energy and Lewis acidity of the xenon fluoride cation.

This study focuses upon the Lewis acid reactivity of XeF(+) with various bases in the gas phase and the determination of the bond dissociation energy of XeF(+). The bond dissociation energy of XeF(+) has been measured by using energy-resolved collision-induced dissociation with neon, argon, and xenon target gases. Experiments with neon target yield a 298 K bond dissociation enthalpy of 2.81 +/- 0.09 eV, and those with argon target give a similar value at 2.83 +/- 0.12 eV. When using a xenon target, a significantly lower value of 1.95 +/- 0.16 eV was observed, which corresponds closely with previous measurements and theoretical predictions. It is proposed that the lighter target gases give inefficient excitation of the XeF(+) vibration leading to dissociation at energies higher than the BDE. Novel xenon-base adducts have been prepared in a flowing afterglow mass spectrometer by termolecular addition to XeF(+) and by reaction of base with XeF(+)(H(2)O). New species have been characterized qualitatively by CID, and it is found that the products formed reflect the relative ionization energies of the fragments. Among the new xenon-containing species that have been prepared are the first examples of xenon carbonyls.