Bond dissociation energies, mass spectrometry

A second role for mass spectrometry in the investigation of reactive intermediates involves the nse of spectroscopy. Althongh an important nse of ion spectroscopy is the determination of thermochemical properties, including ionization energies (addition or removal of an electron), as in photoelectron or photodetachment spectroscopy, and bond dissociation energies in ions, as in photodissociation methods, additional spectroscopic data can also often be obtained, inclnding structural parameters such as frequencies and geometries. 

Guided ion beam tandem mass spectrometry has also been employed to study the reaction of Ni+ with CS2 and COS.2410 The ground state ion Ni+ undergoes endothermic reaction to form NiS+ in both cases, as well as NiCS+ and NiCO+, respectively. Threshold values for the reactions and bond dissociation energies for the products have been determined. 

Hydridophosphino complexes have been described previously (Section 33.2.4). The bond dissociation energy of 209 kJ mol-1 has been measured5 by ion beam mass spectrometry using the reaction in equation (1). The bond energies between V+ and other atoms were compared with the corresponding carbon bonds the energy of the bond to vanadium is about one half that of the corresponding carbon bond. 

Cationic sandwich complexes of the type CpCo(arene) + were first prepared by hydride abstraction from cyclohexadi-enyl cations (Section 7.1). They are accessible in broader variation from the reaction of CpCoX half-sandwich complexes with arene in the presence of AICI3. Their electrochemical reductions to the corresponding 19-electron monocations and to 20-electron neutral complexes have been studied. The stability of electron-rich sandwich complexes increases with increasing alkyl substitution in either ring despite the more negative redox potential mass spectrometry studies of bond dissociation energies of (arene)Co+ complexes corroborate these results. However, neutral sandwich complexes are not very stable in the polar solvents necessary for the reduction of mono- or dications and have been isolated only from alkyne trimerization with CpCo precursors in nonpolar solvents (Section 5.1.4). 

The bond dissociation energies of the alkali metal hydroxides have been determined by several workers from flame studies (9 -11) and by mass spectrometry (1 ). The data for KOH are summarized below. 

The equations used in our study of the thermodynamics and kinetics of thermal electron reactions using the ECD and NIMS are presented. The ECD and NIMS methods were developed in our laboratories. These are used to determine the rate constants, electron affinities, partition function ratios, and bond dissociation energies of molecules and energies for the formation of complexes of anions. The general kinetic model for the ECD and negative-ion mass spectrometry is presented. Molecules will be classified using example data. 

The ability of mass spectrometry to induce chemical transformations makes this method a unique technique for obtaining information about the intrinsic properties of isolated ions and molecules, solvates, clusters, non-covalent complexes, etc. Mass spectrometry is a convenient method for measuring basic thermochemical values of neutral molecules, ions, and radicals. Various molecular properties, such as ionization energy, proton affinity, electron affinity, energy of solvation/ desolvation, and bond dissociation energy can be directly measured in the gas phase by mass spectrometric methods (see also Chapter 2.12). 

Mass spectrometry is a unique method that allows study of the reactivity of isolated metal-containing ions in the gas phase in the absence of solvent. A number of fundamental thermochemical characteristics of organometallic molecules and ions, such as ionization energies, proton affinities, electron affinities and metal-ligand bond dissociation energies, can be determined from mass spectrometry experiments. 

From the infrared spectrum o of SnH4, the estimated bond dissociation energy for Sn-H is 73-7 kcal/mole, which compares well with the value of 70-3 kcal/mole obtained as a mean dissociation energy for Sn-H from mass spectrometry measurements . The thermochemical bond z energy of Sn-H has been obtained as 60-4 kcal/mole. 

Mass spectrometry is one of the experimental methods for determining bond dissociation enthalpies. The mass spectrometer can provide a measure of the appearance potential for a given reaction, that is, the threshold energy necessary to produce a particular set of particles. The appearance potential for the following reaction of H2,... 

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