The microwave spectra of nitromethane and five isotopic species have been investigated Groundstate moments of inertia for the rn = 0 internal rotation state have been used to derive the following structure :Nuclear spin weightings for various I K--m I states, derived using non-rigid group theory, have been confirmed by relative intensity measurements in the microwave spectra. The same theory has been used to explain the unusually large increase (0.060 a.m.u. A") in the inertial defect of CD3N02.The structure and bonding of nitromethane is compared with some related molecules. The structure of the nitro group in nitromethane is shown to fit a series of NOa compounds, between NO; and NO;, where the parameters vary according to the electronegativity of the attached grouping.

The photolysis of trans-t-butyl nitrite in an argon matrix at 20 K gave rise to absorptions due to acetone, nitrosomethane and cis-t-butyl nitrite. Isomerisation was dominant at higher concentrations ; decomposition was dominant at lower concentrations. Vaporisation of nitrosomethane dimer and trapping of the products at 20 K yielded the spectrum of nitrosomethane monomer and the trans dimer. Ultra-violet irradiation dissociated the dimer, leaving nitrosomethane monomer. On warming to room temperature and recooling to 20 K the cis-nitrosomethane dimer was obtained, which could be dissociated by photolysis to regenerate the monomer. A vibrational assignment of the monomer is presented.

The microwave spectra of the iiornial species and seven isotopic species of methyl nitrate have becn measured. The detailed structure of the molecule, which hris a planar heavy-atom skeleton, with the methyl group staggered with respect to the cis oxygen atom, is determined as :$, LO'CHi = 103.4", LO'CHo 110.4", LHoCHo zz 109.8", LCO'N = 112.72", LO'NO(cis) = 118.10", LO'NO(trans) -112.38*.The methyl group and nitro group are tilted away from each other ; the former is inclined at 4.8" to the C-0' bond direction, and the latter at 2.9" to the N-0' direction. The components of the dipole moment have been determined, froni Stark effect measurenients, as pa = 3.07 D, pb r= 0.235 D, pt = 3.08 D, and similar measurements on the trans-180 species have shown that the dipole moment in the normal species is oriented at 39.6" to the bridging N-0' bond. The structure and bonding of methyl nitrate is discussed together with some related molecules ; its structure relates to nitric acid as methyl formate does to formic acid.

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Methods are pmsented for the prepamtion on mole scale of nitmmethane and methyl n i t m t e enriched w i t h q g e n -1 8 or nitl.qgen-15. Enrichment i n each a t h b position i s disnused.