THE LOW-FREQUENCY VIBRATIONAL SPECTRA AND RING-BENDING POTENTIAL OF CYCLOHEXANE AND SOME OXANES

The vibrational spectra of cyclohexane, s-trioxane, p-dioxane, m-dioxane, and tetrahydropyran and a number of their deuterated derivatives are reexamined with particular attention to the low frequency modes. Several difference bands and “hot” bands of these vibrations are observed and assigned. From normal coordinate analysis it is concluded that the six ring bending modes contain little contribution from other valence coordinates. A potential function for ring bending is then developed using the vibrational frequencies and the available information on molecular geometries. A one-fold term in the torsional part of the potential is found to be necessary. The final potential function gives an excellent fit to the frequencies of the low vibrational modes and to the geometries of the molecules considered. The design of a new 39 meter path length cell used in this work is described.