Vibrational spectra of β-cyclotetramethylene tetranitramine and some of its isotopic isomers

Abstract

The infrared and Raman spectra of the β-polymorph of cyclotetramethylene tetranitramine (commonly known as ``HMX'' in the explosives field) and its isotopic isomers, HMX-15NO2, HMX-15N(NO2), HMX-13C(50%), and HMX-d8, have been recorded in the spectral region between 30 and 3500 cm−1. Single crystal polarized Raman measurements on β-HMX were also made in order to separate out modes of Ag symmetry from those of Bg symmetry. Sizable correlation field induced splitting of some of the (NO2) modes was observed. Probable assignments have been proposed for the complex internal vibrations of β-HMX based mainly on the observed isotopic shifts. The spectra of HMX and HMX-d8 in solutions of dimethyl sulfoxide and acetonitrile have also been recorded. The results indicate that the molecular conformation in solution is centrosymmetric and probably similar to that in the β-HMX crystal.