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 A_g symmetry from those of B_g 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.