Dissociation energy of diatomic molecules

Values of average dissociation energies in text Table 2.4 are actually those for the property of bond enthalpy (see Chapter 6), measured at 298.15 K. The bond dissociation energies of diatomic molecules given in Table 2.3 apply at 0 K (absolute zero). 

TABLE 9.4 Some Bond Dissociation Energies of Diatomic Molecules and Average Bond Energies for Bonds in Polyatomic Molecules... 

Bond dissociation energies for diatomic molecules (in color) have more significant figures tiian bond energies for bonds in polyatomic molecules because die bond dissociation energies of diatomic molecules are directly measurable quantities and not averaged over many compounds. 

Strengths of Chemical Bonds, In CRC Handbook of Chemistry and Physics-, CRC Press Boca Raton. Tables with bond dissociation energies of diatomic molecules, bond dissociation enthalpies of polyatomic molecules, and standard enthalpies of formation of (mainly organic) radicals (at 298.15 K). The CRC Handbook is regularly updated, so the tables may vary according to the edition number. 

Table 4 Dissociation energies of diatomic molecules in electron volts (eV)...

Table 2. Dissociation energies of diatomic transition metal, molecules, Dq(M-M) kj mol-1...

The maximum hardness principle also demands that hardness will be minimum at the transition state. This has been found to be true for different processes including inversion of NH3 [147] and PH3 [148], intramolecular proton transfer [147], internal rotations [149], dissociation reactions for diatomics [150,151], and hydrogen-bonded complexes [152]. In all these processes, chemical potential remains either constant or passes through an extremum at the transition state. The maximum hardness principle has also been found to be true (a local maximum in hardness profile) for stable intermediate, which shows a local minimum on the potential energy surface [150]. The energy change in the dissociation reaction of diatomic molecules does not pass through a... 

The first two reactions take place in the gas phase, whereas the third reaction is a wall reaction. The intensity of the emitted light decreases with increase of temperature of the reaction zone due to the increased dissociation of the diatomic sodium molecules. The dissociation energy of this molecule can thus be determined and is in good agreement with the spectroscopically determined value [2]. The rate coefficients for the first three steps indicate that reaction takes place at every collision [2]. The detailed studies deal with the systems sodium/chlorine [12—14], sodium/ bromine [13, 14, 75] and sodium/iodine [12, 13, 15, 76]. It has been noted [2] that preliminary experiments with fluorine suggest considerably slower reactions than for chlorine. 

Inpartictrlar, for the process of dissociation of diatomic molecules stimulated by vibrational excitatiorr, n = max l/2xe. In this case, the total losses of vibrational energy per dissociation event, associated with the non-resonant nature of W relaxation, are equal to the dissociation energy of the molecule ... 

Most of the data derived from spectroscopic measurements have been taken from K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure, Vol. IV, Constants of Diatomic Molecules, Van Nostrand, New York, 1979. Some values for equilibrium bond distances and dissociation energies of dialkalimetal molecules have been taken from G DoteUi, E. Lombardi and L. Jansen, J. Mol. Struct. (Theochem), 276 (1992) 159. 

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