KL- and LK-Vacancy Sharing

For the analysis of systems with more than two states, no analytical solutions exist to describe vacancy exchange. Thus, it appears useful to find out whether two-state models are applicable. Several authors have made the attempt to analyze XL- and LX-vacancy exchange within the framework of two-state models. In particular, the multistate coupling has been described in terms of a series of successive two-state processes.  

In the application of two-state models to XL- and LX-vacancy sharing, controversial results are encountered. It is found that the Demkov-Meyerhof 

It seems that Demkov s model is not well suited for the treatment of asymmetric collision systems. Thus, following the suggestion by Meyerhof et various studies of KL- and LX-vacancy sharing have been performed in terms of Nikitin s model, which has a greater flexibility in describing the orbital energies. Often, the model parameters have been extracted from the fit of the 3 7--4 t MO energy difference obtained from independent molecular orbital calculations. 

Nikitin s model is obviously too small. Reed et pointed out that the values for the exponent from the fit procedure are systematically smaller than those generally used in Meyerhof s analysis. This finding may be explained by the influence of the 2s orbital, which is disregarded in the two-state analysis. In a detailed study of the adiabatic mixing of the related atomic orbitals, it has been shown by Fritsch and Wille that the states 2s and 2p of Kr and Is of Ne are all strongly involved in the formation of the molecular orbitals. In this case the fit procedure by means of a diabatic two-state model is questionable. In fact, without the 2s state the MO data at small R would follow the 2H 2p curve representing the SHM matrix element (18c) as shown further below. 

Figwc 20. Calculations of the 4 r-3 r MO energy difference aad matrix elements ffis2p and 2H,2p for the system Ne -t- Kr. The circles are from HF calculations. The solid and the dashed lines refer to results from Nikitin s model and the SHM matrix elements (18), respectively. 

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