Dissociation energies ionization potentials

Gurvich L (1974) Kondratiev VN (ed) Dissociation energies, ionization potentials, electron affinities, Nauka, Moscow... 

V. N. Kondratiev (ed ). Chemical Bond Dissociation Energies, Ionization Potentials and Electron Affinities, Handbook, Moscow, Nauka, 1962 (in Russian). 

Schexnayder, C. J., Tabulated Values of Bond Dissociation Energies, Ionization Potentials, and Electron Affinities of Some Molecules Found in High-Temperature Chemical Reactions, NBS, Washington, DC, 1963. 

For detailed discussion of those calculations, the reader should refer to the cited references and here we only highlight the most important conclusions of those comparisons. Although we only cited the results of T1 and TIH here, similar results were obtained for other systems and the conclusions are general. The typical errors are thousandths of an A for molecular structure, within 40 cm for vibrational frequencies, and within thousandths (hundredths) of an eV for energetics (atomic and molecular term and level energies dissociation energies ionization potentials electron affinities) at the correlation levels of configuration interaction... 

AHacid values can also be calculated from thermochemical cycles involving measurements of bond dissociation energies, ionization potentials, and electron affinities. Consider the reactions in equations 7.20 through 7.22 ... 

Molecular electronic spectroscopy can provide information on vibrational parameters (frequencies and force constants), rotational parameters (moments of inertia and therefore molecular geometries), electronic excitation energies, ionization potentials, and dissociation energies for ground and excited electronic states. Moreover, a knowledge of excited electronic states is important in understanding the course of photochemically induced reactions. 

The complete removal of an electron from a molecule, i.e. the ionization, requires more energy than electron excitation and has an even stronger effect on the dissociation energy. In Table 4.6 the dissociation and ionization potentials of the first few hydrocarbons have been collected from various sources. It is assumed that ionization is first accomplished through removal of the least bound electron from the highest occupied orbital and also that this orbital embraces the whole molecule. 

These data can be combined with ionization potential (IP) data according to the scheme below to determine bond dissociation energies (BDE). 

For a given molecule and a given intemuclear separation a would have a definite value, such as to make the energy level for P+ lie as low as possible. If a happens to be nearly 1 for the equilibrium state of the molecule, it would be convenient to say that the bond is an electron-pair bond if a is nearly zero, it could be called an ionic bond. This definition is somewhat unsatisfactory in that it does not depend on easily observable quantities. For example, a compound which is ionic by the above definition might dissociate adiabatically into neutral atoms, the value of a changing from nearly zero to unity as the nuclei separate, and it would do this in case the electron affinity of X were less than the ionization potential of M. HF is an example of such a compound. There is evidence, given bdow, that the normal molecule approximates an ionic compound yet it would dissociate adiabatically into neutral F and H.13... 

Distances Ce are in A, dissociation energies in eV (calculated values are not corrected for the 2ero-point vibrational energy, harmonic frequencies Oe in cm , and adiabatic ionization potentials AEip and electron affinities AEea in eV. Experimental values are from Refs. [94, 159-162]. 

In silane discharges, one observes the following when the discharge is off, the mass spectrometric signal at m/e = 31 amu/e (SiH ) as a function of electron energy is due to dissociative ionization of SiHa in the ionizer of the QMS, with an ionization potential of 12.2 eV [312]. The signal with the discharge on is due to ionization of the radical SiHa plus the contribution from dissociative ionization... 

Table 1. Double bond lengths X=X [A] p-p(x) overlap integrals S ionization potentials IP [eV] of the dissociation products XH2 T-bond strengths Erot [kcal mol 1] from the barrier of rotation, calculated at the CASSCF(2,2)/6-31G + ZPE (zero point energy) level of theory.

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