Gas-phase infrared spectra of all eight partially deuterated methyl halides have been obtained; samples were of high isotopic purity. Molecular asymmetry, though quite small, was found to yield significant shifts in the perpendicular structure for the two central Q branches. This was most helpful in the choice of band centers. Observed bands were assigned, including the 72 fundamentals and also 35 overtones and combinations. Although most earlier work was done with samples containing two or more isotopic species, agreement with the present results is quite good in many cases. Evidence for Fermi resonance was found, including two examples in which it occurred below 2000 cm−1. Coriolis coupling between fundamentals was detected in several cases for the fluorides, including a strong resonance between a perpendicular and a parallel vibration. Application of the product and sum rules yielded satisfactory agreement. In a few cases substitution of a heavier atom, such as deuterium for hydrogen, was found to result in an increase for one of the vibration frequencies. However, all such instances involved perpendicular bands in which the choice of origin was quite difficult, and the increases were rather small. Anharmonicity corrections for the partially deuterated fundamentals were computed with the aid of a simple expression, using the corrections employed by others for the C3v molecules. The fundamentals investigated here were compared with values calculated from three different harmonic potential functions for CH3X and CD3X molecules; anharmonic corrections were subtracted from the calculated values. The force field of Aldous and Mills yielded substantially better agreement than an earlier one which was also of the general quadratic type. For the chlorides, bromides, and iodides a Urey—Bradley field was also found to give good agreement with the observed frequencies. In the fluorides the deviations for the Urey—Bradley field were larger than for either of the other two potential functions.

No abstract

By using force constants for both the hydrogen bond H···O–H and the chemical bond O–H in harmonic and Morse potential energy functions, we have obtained ratios of potential energy to macroscopic work of compression for H2O and D2O ice VII using the experimental P–V data of Holzapfel and Drickamer. The Morse potentials gave values of this ratio quite close to 1.0 even at the highest pressure, viz., 165 kbar for H2O and 220 kbar for D2O ice VII. These models all yield the result that the protons remain on their original oxygen atoms during compression; i.e., there is no proton migration with formation of “symmetric” hydrogen bonds. The isothermal bulk modulus for pressures in the neighborhood of 22 kbar, for both H2O and D2O ice VII, was estimated to be 235 kbar.

The diamond and in-plane graphite compressibility data of Lynch and Drickamer are analyzed in terms of simple bond-compression and bond-compression, buckling, and puckering models, respectively, using carbon–carbon stretching and out-of-plane displacement force constants from molecular studies. To the highest experimental pressures of over 300 kbar it is found that the quotient of potential energy of bond compression and macroscopic work of compression, for the same values of the lattice parameter ratio (a/a0), remains essentially constant for diamond at 0.7 indicating that bond compression is the dominant mechanism for storing energy of compression. Similar quotients for graphite at corresponding values of (a/a0) vary from 1.4 at the lowest pressures to 0.6 at the highest for the in-plane bond compression, from 100–4 for the out-of-plane buckling, and from 300–13 for the out-of-plane puckering with the last two modes assuming a fixed C–C in-plane bond distance. It is suggested that in graphite bond compression is the primary mechanism for absorbing intraplanar energy of compression with out-of-plane buckling and puckering much less important until quite high pressures are reached, in contrast to earlier views. This would seem to lead to a partial understanding of the difficulties present in synthesizing diamond from graphite.

No abstract