Forces from absorption spectra response

The observation of a bent Cr-H-Cr bond in the tetraethylammonium salt without an accompanying substantial deformation of the linear architecture of the nonhydrogen atoms in the [Cr2(CO)io(M2-H)] monoanion reflects the inherent flexibility of the bond. The deformability of the[M2(CO)io(M2-H)] monoanion species to adopt an appreciably bent, staggered carbonyl structure was first reported by Bau and co-workers (23) from neutron diffraction studies of two crystalline modifications of the electronically equivalent, neutral W2(CO)9(NO)(m2-H) molecule. Subsequent x-ray diffraction studies (15) of the analogous [W2(CO)io(m2-H)] monoanion found that the nonhydrogen backbone can have either an appreciably bent structure for the bis(triphenylphosphine)-iminium salt or a linear structure for the tetraethylammonium salt, with the W-W separation 0.11 A less in the bent form. Crystal packing forces probably were responsible (15) for the different molecular configurations of the monoanion in the two lattices. In solution, however, all known salts of the [W2(CO)io(m2-H)] monoanion exhibit the same three-band carbonyl ir absorption spectrum char-... 

The forces responsible for a second or third layer to be adsorbed cannot be very strong. We may, therefore, not expect multimolecular adsorption to occur at moderately low relative pressures on flat and homogeneous surfaces. By means of absorption spectra a bimolecular adsorption of p-nitrophenol could be established on CaF2 or BaF2 layers (250). The absorption spectrum of the first layer was quite different from that of p-nitrophenol itself, the absorption spectrum of the second layer being practically the same as that of pure p-nitrophenol. The first layer is apparently sufficiently polarized by the salt surface, to enable a second layer to adsorb the second layer, however, cannot accumulate a third layer. It may not be entirely excluded, however, that there is no more place in the capillary space between the salt layers to accommodate a third layer of p-nitrophenol. 

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