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Normal‐coordinate calculations have been carried out for the molecules acetone, acetone‐d6, acetaldehyde, acetaldehyde‐d4, acetaldehyde‐d1, formaldehyde, and formaldehyde‐d2. Infrared and Raman spectra for acetone, acetone‐d6, and acetaldehyde‐d4 were measured and assigned. Together with experimental data and assignments taken from the literature for the other molecules, these yield an almost complete set of fundamental frequencies.These frequencies were used to derive approximate force fields for these molecules and to investigate the transferability of the force constants. Calculations were carried out with both the Urey—Bradley force field (UBFF) and the valence‐force field (VFF) with selected interaction constants. The Urey—Bradley force field is not satisfactory unless it is augmented with some valence‐force interaction constants. In the valence‐force approximation it is not possible to make an unambiguous choice of the nondiagonal constants. However, a most probable force field is indicated, which on the one hand reproduces the experimental frequencies and on the other hand shows reasonable values for diagonal and nondiagonal force constant.The CO stretching constant, KCO, and the force constants around the CO group appear to be nontransferable among these molecules. The most probable force field indicates a decrease in the value of KCO in going from formaldehyde to acetaldehyde, to acetone. It is noted that the choice of interaction constants has a great influence on the values of the diagonal force constants and on the normal coordinates. Anharmonicity effects are also found to influence the values of the force constants and may affect the resulting conclusions.

The magnetic properties of Co2+ ions in octahedral environment are discussed in relation to the energy-level scheme. It appears that the three low-lying levels arising from the 4F(Γ4) triplet as a consequence of spinorbit coupling are responsible for a temperature-dependent magnetic moment. The expected departure from the Curie-Weiss law is demonstrated by susceptibility measurements on mixed-crystals of CoO and MgO between 300° and 1200°k. From the experimental data the spin-orbit coupling constant for Co2+ in these compounds is estimated to be -136 cm-1.

The surface chemistry of Cr5+ complexes in chromia/silica catalysts for the polymerization of ethene is investigated. To this end not only the chromia/silica system is studied, but also the related combinations chromia/alumina, vanadia/silica and vanadia/alumina. Electron spin resonance spectra are used to follow the rearrangements in the co-ordination of the Cr5+ and V4+ ions, caused by contact with a number of different gases of vapours: H2O, air, CO, C2H4, HCI and NH3. It is found that the atomic arrangement at the surface of some of the systems studied is very flexible and easily influenced by, for instance, contact at room temperature with H2O, HCl or NH3. It is suggested that such a flexibility—encountered especially in chromia/silica—is a prerequisite for the catalytic activity. The active species in the fresh catalyst is Cr5+ in tetrahedral co-ordination. A mechanism is proposed according to which in the initiation step of the polymerization the co-ordination number is increased from four to five. An empty sixth co-ordination site may then be available to accommodate ethene monomers.