Molecular structures diatomic molecules

Data mainly-adapted from G. Herzbeig, Molecular Spectra and Molecular Structure Diatomic Molecules, 1939. 

Herzberg G 1950 Molecular Spectra and Molecular Structure I Spectra of Diatomic Molecules (New York Van Nostrand-Reinhold)... 

Herzberg G 1989 Molecular Spectra and Molecular Structure. I. Spectra of Diatomic Molecules reprint (Malabar, FL Krieger)... 

This difference is shown in the next illustration which presents the qualitative form of a potential curve for a diatomic molecule for both a molecular mechanics method (like AMBER) or a semi-empirical method (like AMI). At large internuclear distances, the differences between the two methods are obvious. With AMI, the molecule properly dissociates into atoms, while the AMBERpoten-tial continues to rise. However, in explorations of the potential curve only around the minimum, results from the two methods might be rather similar. Indeed, it is quite possible that AMBER will give more accurate structural results than AMI. This is due to the closer link between experimental data and computed results of molecular mechanics calculations. 

K. P. Huber and G. Herzberg, Molecular Spectra and Molecular Structure IV. Constant of Diatomic Molecules (Van Nostrand Reinhold Co., New York, 1979). 

The molecular and bulk properties of the halogens, as distinct from their atomic and nuclear properties, were summarized in Table 17.4 and have to some extent already been briefly discussed. The high volatility and relatively low enthalpy of vaporization reflect the diatomic molecular structure of these elements. In the solid state the molecules align to give a layer lattice p2 has two modifications (a low-temperature, a-form and a higher-temperature, yS-form) neither of which resembles the orthorhombic layer lattice of the isostructural CI2, Br2 and I2. The layer lattice is illustrated below for I2 the I-I distance of 271.5 pm is appreciably longer than in gaseous I2 (266.6 pm) and the closest interatomic approach between the molecules is 350 pm within the layer and 427 pm between layers (cf the van der Waals radius of 215 pm). These values are... 

Herzberg, G. and Huber, K. P. (1979) Molecular Spectra and Molecular Structure 4, in Constants of Diatomic Molecules, van Nostrand, Princeton, NJ,... 

Among the diatomic molecules of the second period elements are three familiar ones, N2,02, and F2. The molecules Li2, B2, and C2 are less common but have been observed and studied in the gas phase. In contrast, the molecules Be2 and Ne2 are either highly unstable or nonexistent. Let us see what molecular orbital theory predicts about the structure and stability of these molecules. We start by considering how the atomic orbitals containing the valence electrons (2s and 2p) are used to form molecular orbitals. 

To obtain the MO structure of the diatomic molecules of the elements in the second period, we fill the available molecular orbitals in order of increasing energy. The results are... 

Kotani, M., Texas J. Sci. 8, 135 Proc. of the molecular quantum mechanics conference at Austin Texas, 1955. Electronic structure of some simple diatomic molecules/ Li2, 02 MO-SCF, MO-CI. Slater type orbitals. 

Most values were taken from M. W. Chase, Jr., C. A. Davies, J. R. Downey, Jr.. D. J. Frurip, R. A. McDonald, and A. N. Syverud, "JANAF Thermochemical Tables, Third Edition", J. Phys. Chem. Ref. Data, 14, Supplement No. 1, 1985. A few (in parentheses) came from G. Hertzberg, Molecular Spectra and Molecular Structure, I. Spectra of Diatomic Molecules, and 11. In frared and Raman Spectra of Polyatomic Molecules, Van Nostrand Reinhold Co.. New York. 1950 and 1945. 

From the summary given by G. Herzberg, "Molecular Spectra and Molecular Structure. I. Diatomic Molecules," Prentice-Hall, Inc., New York, N. Y. 1939. 

Huber KP, Herzberg G (1979) Molecular spectra and molecular structure IV. Constants of diatomic molecules. Van Nostrand, New York... 

Usually the electronic structure of diatomic molecules is discussed in terms of the canonical molecular orbitals. In the case of homonuclear diatomics formed from atoms of the second period, these are the symmetry orbitals 1 og, 1 ou, 2ag,... 

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