Diatomic interactions

J. Goodisman, Diatomic Interaction Potential Theory, Vol. I, Academic, New York, 1973, Chap. III.F. 

Kryachko, E. S., and Koga, T. (1985), Modem Aspects of Diatomic Interaction Theory, Academic Press, New York. 

For clusters in the range n =3-8 with 3p excited states, Tutein and Mayne actually observed a predominance of planar or quasi-planar structures. This was interpreted, in terms of diatomic interactions, as due to the strongest binding of... 

Goodisman, J Diatomic Interaction potential theory , Volme I, Chapter 2, Academic Press (1973). 

In the same way that electronegativities determine the polarity of diatomic interactions, ionization radii should define the effective electronic charge clouds that interpenetrate to form diatomic molecules, as shown schematically in Figure 5.3. The overlap of two such spheres defines a lens of focal lengths fixed by the ionization radii, r and r2, at an interatomic distance d = x i + x2-... 

Bond length The Heitler-London method allows the calculation of all first-order diatomic interactions using valence-state wave functions as defined in terms of characteristic ionization radii. 

Plenty of experimental information has been collected for the energy surfaces of atom-diatomic interactions, (see e.g.5 10,12)) Most of the experimental studies were performed on systems like Ar HC1, Ar HF or even heavier analogues for which the number of electrons is prohibitive for accurate ab initio calculations. 

E.E.Nikitin, Ch.Ottinger, and D.V.Shalashilin, Test of the asymptotic method as applied to atom-diatom interaction potentials, Z. Phys. D -Atoms, Molecules and Clusters 36,257 (1996)... 

Schematic representation of atom-diatom predissociation V2(0,0) diatom interacting with an atom, and V2(R) that for a ground state diatom (v,j) (0,0).

More than 20 and 10 years have passed since the publication of two well-known books, Spectra of Diatomic Molecules by G. Herzberg and Diatomic Interaction Potential Theory by J. Goodisman, respectively, which are devoted to the problem of diatomic potential energy functions, or, in other words, the theory of diatomic interactions. Time after time excellent and superior reviews have appeared, and we can refer to the literature of Varshni, Stwalley, Le Roy, Carney, Kolos, Winn, and others. However, their number is not so many. The theory of diatomic interactions occupies the simplest position within the general theory of inter-molecular interactions, for which there remain many theoretical problems. Unsolved problems also concern the theory of diatomic interactions, and the Everest of the complete understanding of the nature of diatomic interactions remains unsubjugated ... 

Probably, the reader thinks that the authors, by analogy, denote the preferable way to Everest s peak. This is not the case here the goal consists in reviewing the modem state of the art of diatomic interaction theory and discussing the currently available tools for the mountaineering, and the reader must continue in pursuit of the peak without the authors assistance, after reading the review presented. To facilitate the reader-mountaineer, the structure of this review article is provided in the following overview. 

What do diatomic interactions themselves represent What is their nature Do there exist means for their approximations with the help of not so complex analytical expressions What is the physical sense, if it exists, of the parameters in such expressions How do they reproduce the real interactions and their corresponding characteristics And so on. In the theory of diatomic interactions there exist a large number of questions which await steps to their final solutions. 

Fig. 1. Typical diatomic interaction potential curve. Turning points corresponding to the energy level E are denoted by circles.

It is evident that the concept of the turning points is purely classical. Nevertheless, it has appeared to be very fruitful in the semiclassical study of diatomic interactions. The set of the turning points for a given diatomic potential reflects sharply its form and is very useful in the construction procedure of a suitable empirical diatomic potential curve. 

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