Infrared spectra from 300 to 10 cm−1 of structure II clathrate hydrates at 4.3 °K

The far infrared transmission spectra of the structure II clathrate hydrates of cyclopropane, oxetane, 1,3-dioxolane, tetrahydrofuran, and cyclobutanone at 4.3, 50, and 100 °K have been recorded. The features have been assigned to translational vibrations of the water molecules and rotational vibrations of the enclathrated guest molecules. The ring puckering vibration of cyclobutanone may contribute to the spectrum, but no evidence was seen of that of oxetane. The density of translational vibrational states of the water molecules is similar to, but shows more pronounced features than, that of the structure I hydrates. The force constants for rotational displacements of the guest molecules arise mainly from steric forces, as is the case in the structure I hydrates. The force constants for 1,3-dioxolane are anomalously high in spite of the fact that the Arrhenius activation energy for reorientation of 1,3-dioxolane in the hexakaidecahedral cage is not.