The infrared and mass spectra of MoO2Cl2, MoO2Br2, WO2Cl2, and WO2Br2 in the gas phase have been studied. The vapours contain mostly monomeric molecules but there is also a small amount of relatively unstable dimeric species present in each case. In inert solvents MoO2Cl2 and MoO2Br2 are dimeric and the infrared spectra are reported. In the solid state all four compounds are polymeric and the absence of the characteristic M = O infrared frequency suggests that only bridging oxygen atoms can be present. X-ray powder diffraction data suggest that the four compounds are isomorphous.

A VE.SCF.CI. calculation of the excited states of nitramide, N-methyl nitramine, and N,Ndimethyl nitramine has been carried out. The assignments for the latter two have been extended to other unconjugated, primary and secondary aliphatic nitramines. All valence electrons, i.e., 6, x-and %-electrons, except for the oxygen atom 2s lone pairs, were included in the calculation. The necessity of including electrons occupying sigma bonds adjacent to the " chromophore " has been illustrated.

The mass spectral fragmentation of RDX and HMX has been described in terms of their metastable transitions, mass measurements and ionization efficiency curves. The ring migration of an NO, group is noted. The known interrelation between the thermal, photochemical and mass spectral fragmentation of RDX is rationalized in terms of the common bond strength inequality CN < NN < NO, which holds for its ground and lowest excited states, as well as the ground and first excited doublet state of its cation. The same rationale applies to s-N,N-dimethyl nitramine and cc-and (3-HMX. This paper has been altered so as to avoid duplication of data on points of agreement, e.g., fragmentation schemes ; only significant differences and new data are noted in detail,

The e.p.r. spectra of polycrystalline RDX, and its single crystals, when irradiated with y-radiation and 254 nm light at 77-298 K, indicate that *NOz may be a primary photochemical product of RDX. Mass spectral analyses of the gaseous products suggested that Nz and NO may also be primary photolysis products of RDX. The identity of these products was consistent with the theoretically predicted bond cleavage patterns of the axial and equatorial nitramine groups of RDX and HMX. A combination of theory and experiment thus permitted the tentative assignment of the primary photochemical steps for polycrystalline RDX.

The VESCF(BJ)-MO electronic bond energies, charge distributions, bond orders, free valencies, and frontier orbital charges, when used as reactivity indices, provide a surprisingly good account of the thermal decomposition and of the electrophilic and nucleophilic substitution reactions of nitramide and primary and secondary aliphatic nitramines. A good account of the chemistry of RDX and HMX is also given by the calculated parameters for s- and as-N,N-dimethylnitramines.