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New high pressure forms of the sesquioxides of holminum, erbium, thulium, ytterbium, lutetium, and yttrium have been obtained by exposure of the C-type sesquioxides to pressures between 25 and 40 kilobars and temperatures between 900 degrees and 1020 degrees C. X-ray diffraction analysis shows that these new high-pressure phases are of the monoclinic B-type which is known for several of the lighter rare-earth sesquioxides (samarium through dysprosium).

The experimental bond energies of atomic and polyatomic metals and intermetallic compounds are reviewed and discussed in terms of various empirical models of bonding, such as the Pauling model of a polar single bond, the valence bond approach for certain multiply bonded intermetallic molecules and the atomic cell model. Illustrations emphasize recent Knudsen effusion mass spectrometric results. For ligand-free diatomic metals a maximum dissociation energy of 640 & 40 kJ mol-I is predicted.

In this study we present all electron ab initio Hartree–Fock (HF) and configuration interaction (CI) calculations of 112 electronic states resulting from interaction between two Fe atoms. The basis set used was of double zeta quality, in general, but the 3d orbital was represented by a triple zeta function. The CI calculations of the ground state included sixtuple excitations from a reference configuration. The calculations were performed to the same degree of accuracy for all the 112 low-lying states. The ground state is a 7Δu state with the configuration (3dσg)1.57(3dπu)3.06(3dδg)2.53 (3dδu)2.47(3dπg)2.89(3dσu)1.49 (4sσg)2.00. The equilibrium distance is calculated to be 4.54 a.u. (2.40 Å), and the vibrational frequency to be 204 cm−1. The chemical bond between the iron atoms is a single bond, and it is almost entirely due to the 4sσg molecular orbital. The ’’band’’ of the 112 low-lying states make a large contribution to the partition function, resulting in a lowering of the experimental dissociation energy of the Fe2 molecule. Our mass spectrometric measurements essentially confirm the previous results by Lin and Kant. The experimental dissociation energy D0° of Fe2 has been determined as 18±4 kcal mol−1 or 75±17 kJ mol−1. The corresponding standard heat of formation is 180.5±4 kcal mol−1 or 755±17 kJ mol−1.

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