Microwave Spectrum of Methyl Nitrate

Abstract

The ground‐state rotational constants of methyl nitrate show that the five heavy nuclei of the molecule lie in the same plane. The hydrogen atoms of the methyl group are found to be staggered with respect to the nearest oxygen of the NO₂ group. Stark effect measurements yield a dipole moment of 3.10±0.05 D. Satellites arising from excited states of the torsion of the NO₂ group were observed. Rough relative intensity measurements yield a frequency of 130±20 cm^—1 for this normal mode and a barrier of 9100±2600 cal/mole. This would seem to indicate a significant amount of double‐bond character in the CO–N bond. The barrier to internal rotation of the methyl group, as determined from torsional satellite splittings, is 2321 cal/mole. A large discrepancy exists between the experimental and statistical entropies, the reason for which is not clear. Satellites arising from the combination first excited states of the methyl and NO₂ torsions have an anomalous appearance on the basis of the single internal rotor theory. A qualitative explanation for this is obtained when the theory is extended to include the torsion of the NO₂ group.