INTERNAL ROTATION BARRIER AND DIPOLE MOMENT OF METHYL NITRATE

Author Institution: Department of Chemistry, Harvard UniversityThe microwave spectrum of methyl nitrate has been studied in the region of 8,000 to 36,000 megacycles. The moments of inertia of the normal aperies lead to the conclusion that the the five heavy atoms of the molecule lie in one plane. Many satellite lines have been observed which are due to three or possibly four different normal modes of vibration. Splittings in the satellites belonging to the first and second excited states of the methyl group torsional vibration show that the barrier to internal rotation of this group is 2,300 cal/mole. Satellites have also been observed which appear to be due to the simultaneous first excitations of both the methyl group torsion and the $NO_{2}$ group torsion. The measured splittings in these satellites show that the barrier to internal rotation of the methyl group is about 1,800 cal/mole when the molecule is in the first excited slate of the $NO_{2}$ group torsion. The possible significance of this in terms of the origin of the barrier will be discussed. Preliminary work on the dipole moment gives 3.06 D as the component along the axis of least moment of inertia and a value of the order of 0.2 D along the axis of intermediate moment of inertia. The third principal axis is perpendicular to a plane of symmetry. The research was made possible by support extended Harvard University by the Office of Naval under ONR Contract Noar 1866. Task Order XIV