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Nonempirical LCAO MO SCF calculations are reported for the ground, C 2 " states of the Group IIa dihalides, BeF 2 , MgF2' and CaF 2 . These calculations demonstrate the importance of 3d orbitals in the bonding trends of the dihalides and, hence, in the determination of the equilibrium bond angles and the bending force constants. The calculations on BeF 2 indicate that d orbitals play an important role in the bonding but do not preferentially alter the general features of the total energy curve at any bond angle. In the case of MgF2' d orbitals are found to preferentially lower the energy of the nonlinear configurations. However, for both species, the ground-state equilibrium bond angle is predicted to be 180°. Configuration interaction studies also support the fact that, in the gas phase, the linear configuration is most stable. On the basis of s (1 s, 2s, 3s, 4s, 2p, and 3p orbitals on Ca) basis set calculations, it is predicted that CaF2 is linear. However, when 3d orbitals are added to the s basis set, the predicted equilibrium bond angle is 145°. This is in good agreement with the value of 141° deduced from matrix-isolation spectroscopy. The bonding in these molecules is discussed with reference to the nonempirical molecular correlation diagram.

AbstractsA large configuration-interaction calculation has been performed to determine the wave function, energy, and molecular properties of CO. The most important configurations were used to obtain the natural geminals and their occupation numbers. A pair-energy approach to the correlation energy was attempted with results which differ significantly from the configuration-interaction results.On a fait un calcul CI avec un grand nombre de configurations, pour CO pour dCterminer la fonction d'onde, 1'Cnergie et des proprittts diverses de cette moltcule. Les configurations les plus importantes ont Ctt employtes pour obtenir les gtminales naturelles et leurs nombres d'occupation. On a essay6 aussi de faire un calcul de l'tnergie de corrtlation en partant des tnergies des paires, ce qui a donnt des rksultats qui diffPrent considtrablement de ceux obtenus par la mCthode CI.Eine grosse Konfigurationswechselwirkungsberechnung wurde fur CO ausgefuhrt, um die Wellenfunktion, die Energie und verschiedene Eigenschaften dieses Molekiils zu bestimmen. Die wichtigsten Konfigurationen wurden angewandt um die natiirlichen Geminale und ihre Besetzungszahlen zu berechnen. Die Korrelations-Energie wurde auch mit eine Paar-Energie-Methode aufgeschatzt, was doch Resultate gab, die sich ansehnlich von denen die mit der Konfigurationswechselwirkung erhalten wurden, unterscheiden.

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A potential energy surface for the Ne–H2+ reaction has been obtained in the LCAO–MO–SCF approximation. Analysis of the surface indicates that the reaction Ne+H2+→NeH++H should proceed with an endoergicity of 12 kcal/mole, in agreement with the experimental results of Chupka and Russell. Several procedures for parameterizing a diatomics-in-molecules (DIM) representation of the NeH2+ surface are considered. The results show that an accurate representation of the SCF surface can be obtained from the DIM model using a minimum of diatomic and triatomic data.