Molecular orientation accuracy

In what follows we will establish under which conditions and to which accuracy the approximation (4.3.38) is justified for the cases of normal, parallel, and inclined molecular orientations with reference to the surface plane.186... 

However, both equations need improvements, and none of these equations at this stage can be used for the prediction of critical surface tension or surface tension of a polymer with sufficient accuracy. The problems of the difficult assignment of the thickness of the monolayer at the interface, of the molecular orientation, of crystallinity and of hydrogen bonding could contribute to the sporadic results regarding the calculated critical surface tensions. 

Sokolowski and Steele have adapted the spherical harmonic expansion technique described in Section III.A to the calculation of the density profiles of nonspherical molecules in contact with solid surfaces. They have used the results to investigate molecular orientation effects in high temperature adsorption from the gas phase. The RAM theory described in Section III.E has been extended to the adsorption of fluids on solid surfaces by Smith et al. ° for hard-sphere interactions and by Sokolowski and Steele to the case of more realistic fluid-solid interactions. The principal deficiency of the approach is the accuracy of the predicted correlation functions for the bulk fluid which are required as input to the theory. 

Theoretical calculations are valuable tools for analysing solid-state 170 NMR spectra. As mentioned in Section 4.1, for example the absolute orientations of 170 NMR tensors in a molecular frame can be readily determined by ab initio calculations. However, a key problem of "accuracy" always receives attention. In many papers in the literature, the calculated results for the magnitudes of 170 CS tensors are compared with those of experimental data. It seems that the quantum chemical approach is the most frequently used and can yield reasonable... 

---