Theoretical Dissociation Energies for Ionic Molecules

Abstract

Ab initio calculations at the self-consistent-field and singles plus doubles configuration-interaction level are used to determine accurate spectroscopic parameters (D e , r e , u e ) for most of the alkali and alkaline-earth fluorides, chlorides, oxides, sulfides, hydroxides and isocyanides. Numerical Hartree-Fock (NHF) calculations are performed on selected systems to ensure that the extended Slater basis sets employed for the diatomic systems are near the Hartree-Fock limit. Extended gaussian basis sets of at least triple-zeta plus double polarization quality are employed for the triatomic systems. By dissociating to the ionic limits, most of the differential correlation effects can be embedded in the accurate experimental electron affinities and ionization potentials. With this model, correlation effects are relatively small (0.0-0.3 eV), but invariably increase D 0 . The importance of correlating the electrons on both the anion and the metal is discussed.The theoretical dissociation energies (D 0 ) are critically compared with the literature to rule out disparate experimental values. The theoretical studies combined with the experimental literature allow us to recommend D 0 values that are accurate to 0.1 eV for all systems considered. The systematic treatment of many different systems reveal many trends. For example, the dissociation energies of the alkali and alkaline-earth hydroxides are observed to be less than the corresponding fluorides by just slightly less than the difference in electron affinities of F and OH. In general, there is a strong correlation between the dissociation energy (to ions) and r e , because the bonding is predominantly electrostatic in origin.

Theoretical Study on the Reaction Mechanism of CO2 with Mg

“…Looking into another source of thermochemical data, CRC Handbook of Chemistry and Physics , we find the value of 86.8 ± 3.0 kcal/mol for the bond strength in MgO. Earlier ab initio calculations by Bauschlicher and co-workers resulted in 63.4 kcal/mol which is much closer to the QCISD(T)/6-311+G(3df) value than to the experimental results. The existing uncertainty concerning the bond strength and standard heat of formation for MgO prompted us to reinvestigate energetics of this molecule using highly accurate multireference configuration (MRCI) method …”

Estimation of thermodynamic and physicochemical properties of the alkali astatides: On the bond strength of molecular astatine (At2) and the hydration enthalpy of astatide (At−)

“…The agreement between the Herzberg and Brewer and Brackett values (columns (g) and (h)) is striking and we have used the average of these values in our analyses. The measurements of Brewer and Brackett 43 are also in good agreement with theory 48 . We stress that our conclusions do not change when the other (slightly different) values are used.…”

“…The measurements of Brewer and Brackett 43 are also in good agreement with theory. 48 We stress that our conclusions do not change when the other (slightly different) values are used.…”

A Valence Bond Study of the Bonding in First Row Transition Metal Hydride Cations: What Energetic Role Does Covalency Play?

“…With the minimal VB structure set, the VB wave function correlates with restricted open-shell Hartree−Fock (ROHF) states of the TM + and H. Because the HF level treats poorly the atomic states and especially the 3d n +1 state, the deficiencies in the atomic calculation will carry over to the BDE values, even if the molecular calculation is correct. Goddard et al − and Bauschlicher et al , showed that the deficiencies can be avoided by correcting the energies of the TM + fragment using experimental atomic data. Thus, the TMH + species are dissociated into the atomic electronic states most closely resembling their situation in the molecule (i.e., for TM + it is the 4s 1 3d n state), and whenever necessary, the experimental atomic state splitting is used to correct the energy of the TM + fragment to the corresponding atomic ground state.…”