Spectroscopic study on deuterated benzenes. I. Microwave spectra and molecular structure in the ground state.

Abstract

We observed microwave absorption spectra of some deuterated benzenes and accurately determined therotational constants of all H/D isotopomers in the ground vibrational state. Using synthetic analysis assuming that all bond angles are 120°, the mean bond lengths were obtained to be r[0](C–C) = 1.3971 Å and r[0](C–H) =r[0](C–D) = 1.0805 Å. It has been concluded that the effect of deuterium substitution on the molecular structureis negligibly small and that the mean bond lengths of C–H and C–D are identical unlike small aliphatic hydrocarbons, in which r[0](C–D) is about 5 mÅ shorter than r[0](C–H). It is considered that anharmonicity is very small in the C–H stretching vibration of aromatic hydrocarbons.