X-ray Emission Spectroscopy of Nitrogen-Rich Compounds

Abstract

Nonresonant X-ray emission spectroscopy was used to compare the nitrogen-rich compounds ammonium nitrate, trinitrotoluene, and cyclotrimethylene-trinitramine. They are representative of crystalline and molecular structures of special importance in industrial and military applications. The spectral signature of each substance was analyzed and correlated with features in the electronic structure of the systems. This analysis was accomplished by means of theoretical simulations of the emission spectra and a detailed examination of the molecular orbitals and densities of states. We find that the two theoretical methods used (frozen-orbital density functional theory and real-space Green's function simulations) account semiquantitatively for the observed spectra and are able to predict features arising from distinct chemical complexes. A comparison of the calculations and the data provides insight into the electronic contributions of specific molecular orbitals, as well as the features due to bandlike behavior. With some additional refinements, these methods could be used as an alternative to reference compounds.

Quasiparticle lifetime broadening in resonant x-ray scattering ofNH4NO3

“…Unsurprisingly it is strongest at excitation energies which exhibit a strong peak associated with the NO π bonds (though polarized emission spectra would separate these two). The extreme broadening observed in experiment stands in stark contrast to previous XES calculations [45] or the band structure in Fig. 1 which indicates that the NO σ bands have almost no dispersion.…”

Origins of extreme broadening mechanisms in near-edge x-ray spectra of nitrogen compounds

“…2 AN provides a useful test bed for crystalline molecular solids, containing both a strongly reduced and strongly oxidized nitrogen, in different geometries, in a relatively small unit cell. This diversity leads to different phonon coupling and electronic structure, the effects of which are interleaved in the observed spectra.…”

Local time-correlation approach for calculations of x-ray spectra

“…As discussed in Ref. 27, the lower intensity with respect to experiment in the 385-390 eV region is due to an underestimation of the transition intensities associated with σ NC bonds. In general, intensities associated with σ bonds are more affected by vibrational distortions (not included in our simulations) than π bonds.…”