A theory of vibrational frequency shifts revisited: application to dimers of LiH with the inert gases He, Ne, Ar and Kr
Titel:
A theory of vibrational frequency shifts revisited: application to dimers of LiH with the inert gases He, Ne, Ar and Kr
Auteur:
McDowell, Sean A. C. Buckingham, A. David
Verschenen in:
Molecular physics
Paginering:
Jaargang 103 (2005) nr. 2-3 pagina's 257-262
Jaar:
2005-01-20
Inhoud:
The objective of this paper is to contribute towards an understanding of the anomalous blue vibrational shifts that have been observed on forming some hydrogen bonds. It is shown that linear complexes of the LiH molecule with an inert gas atom Rg exhibit red or blue shifts of the LiH vibrational frequency depending upon whether Rg is attached to the Li or the H atom. The shifts in the frequency of the Li-H vibration on forming the weakly bound linear complexes Li-H…Rg and H-Li…Rg (Rg = He, Ne, Ar, Kr) were determined by ab initio computations at the MP2/6-311++G(2d, 2p) level of theory. These frequency shifts were found to be in good agreement with predictions from a model based on perturbation theory and involving first and second derivatives U' and U'' of the interaction energy with respect to displacement of the Li-H bond length from its equilibrium value in the isolated molecule. Concentration of the Li-H vibrational motion in the light H atom causes U' and U'' to be dominated by repulsion in Li-H…Rg and by attraction in H-Li…Rg, producing blue and red shifts, respectively. The bond length changes on complexation are well predicted by U'.
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