Quantum chemistry of confined space-the nanovessels

Molecules at long distances interact through the mediation of the electric fields created by them. The valence repulsion is of a different character, since it results from the Pauli exclusion principle, and may be interpreted as an energy penalty for an attempt by electrons of the same spin coordinate to occupy the same space (cf. Chapter 1 and p. 516). 

Luty and Eckhardt have highlighted the role of pushing one molecule by another. Let us imagine an atomic probe, e.g., a helium atom. The pushing by the probe deforms the molecular electronic wave function (Pauli deformation), but 

Eckhardt, in Reactivity of Molecular Solids , eds. E. Boldyreva, V. Boldyrev, Wiley, 1999, p.51. 

Now imagine a lot of atomie probes eonfining the space (like a cage or template) available to a moleeule under study. In such a case the molecule will behave differently from a free one. For example, 

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