Experimental and calculated bond dissociation energies

Table I Experimental and Calculated Bond Dissociation Energies (in eV) for Homonuclear Diatomics

Table 14 Calculated and Experimental Metal-Carbon Bond Dissociation Energies Dq (kcal/mol) of Group 11 and 12 Methyl and Phenyl Compounds Using Stoll—Preuss Pseudopotentials Geometries Optimized at MP2/SP2 (see Table 12) 

The calculated bond dissociation energies are in good agreement with experiment except for difluorine. The theoretical result Dq = 46.0 kcaPmol is higher than the experimental value of Do = 36.9 kcaPmol. The trend however, that the BDE of F2 is smaller than the bond dissociation energies of CI2 and Br2 is preserved. Table 13.3 shows that the values of both and increase steadily from I2 to F2. We want to point out that 

We first give calculations of these four molecules with an ST03G basis. The total energies and first bond dissociation energies are collected in Table 13.1. We see that, even with the minimal basis, the bond energies are within 0. 4 eV ofthe experimental values except for CH3, which has considerable imcertainty. The calculated values tend to be smaller, as expected for a minimal VB treatment. 

We will now look at how different types of wave functions behave when the O-H bond is stretched. The basis set used in all cases is the aug-cc-pVTZ, and the reference curve is taken as the [8, 8J-CASSCF result, which is slightly larger than a full-valence Cl. As mentioned in Section 4.6, this allows a correct dissociation, and since all the valence electrons are correlated, it will generate a curve close to the full Cl limit. The bond dissociation energy calculated at this level is 122.1 kcaPmol, which is comparable to the experimental value of 125.9 kcal/mol. 

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